The importance of the Severan campaigns in Scotland and information about them has been slowly accruing over the past 30 years not least due to the efforts of J.K St. Joseph and aerial photography techniques which have shown up hitherto unknown sites and has indicated in general terms the line of march of campaigns. While discussion continues about the dating of some camps and proof of an absolute nature is lacking, it is widely held that, north of the Forth, the double line of 63 acre marching camps and the single line of 120 acre camps, in the main date to the Severan period and reflect the two brief campaigns against the Caledonians in 209 and 210 AD. It is the general premise of this paper that the route taken, leaving out controversy about individual camps, throws light on the general nature of the campaign and the military strategy lying behind it.

The Route
Two extremely rare coins minted on the occasion of the military campaign in Scotland give us invaluable evidence for the route of march north to area of operations.
The coins themselves have given rise to a certain amount of controversy, since various authors (eg. Reed, Birley ) have used the coins as evidence of particular routes of march and locations of bridges, while at the same time committing errors in the dating of the Caracalla coin. The divergence of one year between the coin of Severus and that of Caracalla, which apparently makes the theories they propose less likely, may have an explanation but more about that later. Discussion of this issue is not new and in fact Oman as long ago as 1931 presented a hypothesis of a Forth river crossing.

The crossing about which much less doubt exists is that of the Tay at the point of the legionary base at Carpow. What has caused problems for academics is that while these two points are extremely logical crossing points and suggest themselves as solutions of which rivers are celebrated in the two coins of Septimius and Caracalla, finding a feasible crossing point on the Forth for the bridge depicted in Caracalla's coin has remained somewhat problematic. It is of course possible that Caracalla's bridge of boats was the bridge over the Tay and that Septimius built a fixed construction over the Forth but this raises bigger problems. A bridge of boats at Carpow over the Tay is entirely feasible but it is almost impossible to find a point on the Forth where a fixed construction would be a) technically possible and b) big enough to be worthy of commemoration in the issue of a coin. It is probably as a result of this difficulty that many authors have opted for the bridge of boats at Carpow on the Tay and then, given the near impossibility of finding a logical point for a fixed bridge on the Forth, have argued that this construction was located far to the south in England.
However, if a bridge were not constructed across the Forth then one would have expected to find more sign of re-use of forts and camps inland as the army marched round the obstacle of the natural barrier. Apparent lack of activity inland seems to indicate an eastern route and the fact that a bridging of the Forth was made at some point. Difficulty about the placing of the two respective bridges may lead some to take refuge in the attribution of a general propaganda value to the coins without a specific historical reference. Such a view is directly countered by A.S. Roberston, who, while not a partisan of any particular placing of the bridges, indeed, who argues that the coins may refer to a series of bridge-building activities, makes the observation that the coins do not belong to substantive issues but indeed to a very rare type of special issue. The important point that the "bridges" do not conform to the substantive type of coinage which had several general and often recurring themes does seem to indicate that there is a direct historical reference, whether they indicate just two particular bridges or whether as she says, that such issues may not have referred to specific bridges but may celebrate the "crossing of any great river in the Caledonian campaigns." In summary then it is clear that there is no outright indication where such bridges were built if indeed the two coins refer to two specific bridges and not to a whole series of bridge building activities in general as for example characterise the accounts of Cassius Dio and Herodian. Some of the main hypotheses proposed for the position of such bridges, put forward with varying degrees of force may be listed as follows: 1) Birley - Carpow on the Tay and the Forth, later changed to Carpow and perhaps the Tyne or York in the north of England. 2) Reed - Carpow on the Tay and the Forth near the present railway bridge. 3) Robertson - not especially involved in attribution of sites but perhaps the Tay and for the coin of Septimius suggests York, Severus' base in England. 4) Oman - crossing of the Forth either at Alloa or Airth. Oman was not aware of the second coin, issued by Septimus, at the time he wrote his treatise though he postulated the existence of such a coin, though in terms of a celebration of the same crossing as shown on the Carcalla coin. While it is not critical to my overall argument exactly where such bridges were constructed, I do think it is fair to admit that my tendency is to favour those views which see the Forth and Tay as the most likely areas. First of all I am completely unconvinced of the likelihood of an invading emperor undertaking major engineering projects in an area already completely under his control for some time. If such work had been necessary it could have been done in advance of the campaign. Furthermore the proposed alternatives for the fixed construction, at either York or on the Tyne, are areas which in no way are seen as being fundamental to the support of the campaign further north. To be clearer, the supply of the army in the north was centred on South Shields at Arbeia with supplies being organised from there for onward transport by sea to Cramond on the Forth and the Tay estuary. There is no archaeological evidence that supplies were transported in any quantity overland despite a new granary having been constructed at Corbridge further up the Tyne. Even Birley, who proposes land supply of the army running north up from Corbridge argues for water borne transport from the coast via barges and lighters, thus somewhat diminishing whatever utility a bridge over the Tyne might have had. Thus I am somewhat sceptical of any view which proposes an English site for the bridge represented on the coin of Septimius. It seems to me also of dubious propaganda value to celebrate building a bridge in "friendly" territory hundreds of miles south of the actual problem area. A bit like, to take a modern analogy, of celebrating alliance troops landing in Saudi Arabia in the war against Iraq. With regard to the difficulty that the corrected dating of the Caracallan coin poses to the theory of Reed I feel that the hypothesis proposed by him is still a valid one and should not be dismissed and suggest the following explanation to account for the "reverse dating" of the two coins. If it is accepted, at least as a hypothesis, that Caracalla crossed the Forth with a pontoon bridge and Septimius crossed at Carpow with a fixed construction the question is then raised about the dating of the coins because that of Caracalla is dated 209 AD and that of Septimius as 208 AD. One solution is that the Roman forces were split right from the outset and that the building programmes were concurrent. This is not so unlikely given that the area of the Meateae was quiet at the time and that Severus and Caracalla enjoyed completely unhindered mobility at sea from which to supply both operations without the need for the connecting land link between them. Thus is could be that Caracalla was busy building his bridge over the Forth while at the same time Septimius was building his further north over the Tay. The difference in the dating on the coins could then be due to the bridging of the Forth taking much longer that of the Tay.

The Reason
What lies at stake with this question of the two bridges? Clearly, even if we cannot be sure of the geographical location of them, these massive projects must have been carried out with some important motive or purpose behind them. It is my contention that we can thus learn something of the strategy of the campaign because, difficult as the question may be, we must immediately ask why? Why build two large scale engineering projects when other routes existed into the north of Scotland? This question becomes even more pressing when one considers that another campaign with which it had many similarities and which must have been consciously in Severus' mind and which also used seapower, though to a lesser degree I believe, did not see the need to build any large structures of the type we see depicted on the two coins of Severus and Caracalla. I am of course talking about the military campaign of Agricola who by taking a more inland route by Stirling and then through by Strageath and the Strathearn valleys, followed a more logical and easier route than it seems Severus did. It seems to me that the only logical answer to this question is tied up with the nature of the route by which Severus was being resupplied. Basically Severus, like any military commander, did not want his supply routes to be cut and since his supplies were coming by sea that meant keeping the land between his army and the coast free from enemy. Since this was all but impossible in certain marshy areas of which we have accounts by Dio and Herodian, where the Caledonians had the upper hand, he had to build extensive bridges across the marshy areas to keep his access or contact with the fleet unimpaired. As Oman cogently put it some time ago:- "The answer to this query must, I think, be as follows - using Herodian's narrative as our basis of explanation. The army, when it had established its main base camp at Cramond, and had no doubt also occupied some of the ruined forts on the Antonine Wall from Abercorn westward, was being worried by the raids across the inaccessible marshes of which Herodian speaks, i.e. by the Caledonians crossing the boggy, muddy flats between Stirling and Alloa, so as to cut into the Roman contonment area. And if Severus had resolved to advance by the old road, via Bannockburn and Stirling, he would have left these tiresome points of attack between him and his fleet and the base at Cramond, since he had gone so very far inland." Any glance at a map will show that with bridges in these two positions a very direct route is made possible up the east coast with contact between the army and the fleet being viable. Having the army within easy reach of the seas surely meant that as re-supply was much easier it could move much more quickly. Thus such a possibility would additionally give an advantage in speed and power. Whether motives of haste were present we can not be sure though certainly the historical sources lay an emphasis on speed but this could equally be a standard formula and the historical sources are also not altogether reliable. One can only speculate perhaps but feelings of mortality may also have played a part. The account by Cassius Dio of Septimius knowing when he left Rome that he would not return may or may not be later interpretation or exaggeration but we do know Septimius was superstitious and it may be that he had premonitions of the course events were to take. Military strategy might also have played a part and certainly Septimius knew, even from the beginning of his reign, just what an important factor speed was in combating an enemy. Equally having the ability to be supplied by sea meant that more troops were freed for combat rather than transport duties. Thus factors of speed and strength are both involved in this hypothesis as well as security of supply routes. It seems to me pertinent to take into account what we know of Severus' general character in that he is known to be a "propagator imperii" and not one to cede territory; that coupled with the fact that, superstitious or not, he must have known that he was on a race against time and wanted to get as much done, better, get the affair settled as quickly as possible. The mobile seaborne invasion was his solution to the situation. Such a strategy and mindset might also supply an explanation for the fact that the Lowlands of Scotland were not garrisoned. Much has been made of the temporary aims of Septimius on the basis of his failure to garrison the Lowlands but the archaeological evidence at Carpow, with clear evidence that a long term stay was envisioned, makes such a position hard to sustain whatever may have subsequently happened under Caracalla. Reed, alternatively, suggests that failure to garrison the Lowlands was due to his confidence of victory in the north. However, this last view is not incompatible with my emphasis on the marine nature of the campaign as strength and flexibility could only but increase the confidence that Reed attributes to Severus. If, as Birley has stated, Severus in all probability was very much aware of the achievement of Agricola before him through links by way of relatives and acquaintances to direct knowledge of Agricola's governorship and his historian Tacitus, then it is hardly surprising that there should be similarities in their campaigns and it cannot be doubted that Severus must have wanted a similar outcome for his campaign. With regard to probable troop levels it must be assumed that the emperor would have more troops available than Agricola did, for, if one thing is certain, the one thing the emperor would not intend to suffer, is a defeat. Therefore it might not be too surprising if a field army in excess of 30,000 men was assembled. Fort and camp positions, ports and of course the previously mentioned use of naval supply and support are all points of general similarity between the two campaigns. While it is true that the nature of the terrain in many cases would indicate similar solutions to people working completely independently of one another, it does raise the question as to how much information Severus had available to him from previous campaigns and in particular from Agricola's. Given Birley's point earlier and the fact that Septimius seems to have committed himself to naval dependance at an early stage, my suspicion is that he had a great deal of information already to hand before the campaign started. We know that Agricola had gathered a great deal of naval information around the coast of Scotland in precisely this region to such an extent that the army and navy often shared the same camps at night. It is worth mentioning that the double line of 63 acre camps which runs up the east coast of Scotland converge precisely in the area of the Montrose basin, where Agricola had a port at Dun. As the nearest of the Severan marching camps (that we can be sure of) is only about 10 miles away from the old Agricolan port it is stretching the imagination I think, too far, not to suppose that Severus too, made use of the harbour there even if he didn't re-occupy the Agricolan camp there. Following my basic premise from the outset, it may be that not only the route of advance up the east coast of Scotland but the very positioning of Carpow, can give us some insight to the strategy and development of the campaign. The site at Carpow has been variously identified and there have been those who have generally accepted the idea that it could have been the Orrhea of Ptolomy's cartography and the later Horrhea Classis of the Ravenna geographer. It has also been stated at times that Agricola may have used it in his navigation of the area. In fact this is somewhat understating the case as the following assertion makes clear:- "Furthermore the map accentuates a point in strategy that was gradually becoming clear without its aid. The centre of gravity in Flavian times in Scotland did not lie on the isthmus between Forth and Clyde as in later days but rather in the Earn valley. We may observe in this connection that the one port on the Forth at this time was Colanica. But the great port Horrea, with the military store-houses, the port which everyone knew, stood on the Tay, with yet another river port, Tamia, behind it." It is certain that Agricola did in fact know the river estuary very well but I feel the identification of Carpow as Agricolan, to say nothing of his major naval base the Horrea, has to be questioned for several reasons. The most basic is that the archaeology of the site and aerial photography has failed to produce any indication of an Agricolan period for the location. Secondly it would not have been a good site for a stores base despite claims to the contrary since the surrounding area is low lying, marshy and thus subject to being easily cut off from the army which needed the supplies. Thirdly, as far as Agricola is concerned, his main army base was some distance upstream at Inchtuthil and a stores base at Carpow left several rivers to cross quite apart from the distance and the dubious nature of the terrain. Thus Agricola did have good reason to want to get his supplies up the Tay as far as he could to supply the legionary base at Inchtuthil. How far he managed to get upstream is an open question but on the basis of the archaeological evidence he didn't use Carpow. Assuming that navigation was possible up to Perth, even if necessitating the use of smaller craft, it indicates that Carpow was not chosen as has been suggested, because it was the highest point of navigation but for other reasons, though it may well be true that it was the highest point of safe navigation for large vessels, as in fact it has been until recent times. This may, however, be almost coincidental and it may be that Carpow represented, not so much the highest point of safe navigation for Severus, but the lowest point of easy bridging of the river. Severus in fact, probably had every reason for wanting to keep his bases near the coast and given the difficulties of navigation on the Tay, it is probable that the choice of Carpow as the legionary base involved factors other than simply navigability. Indeed if Septimius had built his bridge over the Tay even a small distance upstream the actual size of the bridge necessary would have been much reduced though probably involving longer approaches through marshy ground, while a few miles upstream the Tay is mere fraction of its width. Where Carpow stands the Tay is already broadening out and even a very small distance further downstream would involve a completely different scale of project. Thus there are indications that, just as I have posited for the case on the Forth, the motive in the positioning of the bridges has more to do to with an "eastward vector" than looking for easy bridging points. As with the Forth, we can once again see, that to the west there are marshy areas where the Romans could be at a tactical disadvantage and which they certainly would not want to be positioned between them and the fleet. Other factors in choosing Carpow as the site of the legionary base might certainly be that it was near the local pictish capital of Abernethy and it was often Roman policy to locate bases near local political centres. Equally it was fundamental that it could be resupplied from the sea by navigating up the river Tay. Without the resupply from sea it would have been problematic as a base as the very attribute which made it a good defensive position, equally made it susceptible to being cut off from the other nearest Roman forts near Perth. The main point I would like to make here is that there is more than a little evidence to support the view that, should it be have been considered necessary, it would have been possible to navigate further up the Tay than Carpow. Whether this involved using smaller coastal craft is not important at this juncture. Agricola would have had a good motive for getting his supplies as far upstream as possible and it seems that he did. This therefore seems to indicate that the motive for choosing Carpow as a site, was not governed by sheer navigability but by other motives, possibly some of those that have been discussed here. From the foregoing it is clear that I attribute a primary and determining role to the navy in the campaign. However it may be that the makeup of the navy itself can shed some light on the events on land. Perhaps subconsciously there might be the tendency to think of the addition of the Danube and Rhine flotillas to the Classis Britannicus simply as more of the same but this is unlikely to be the case. The vessels of the Danube have normally been pictured as quite tubby and those of the Rhine as flat bottomed lighters, typically drawing about 7 feet and being able to carry about 50 tons. What were all these vessels used for? Birley suggests in his book that there were lightermen from Mesopotamia based at Arbeia who used small craft to ferry supplies up to Corbridge. From there the supplies were off- loaded and then taken north up Dere Street to their destination at the Forth. This idea, while being quite possible, lacks any backup at the archaeological level. Such an operation would involve continuous wagon loads of material being transported over a two year period (or to be more precise, over two military campaigns extended over a two year period) and one would expect to find either reoccupation of the forts along the way or the building of new ones. Neither case has been found. The line of temporary camps running up the same route are just that, temporary camps and probably indicate the line of march of Caracalla's campaign which he led against the Maeatea in 210. In the Firth of Forth such vessels would not come into their own until they got to the upper reaches of the Firth as mentioned in Oman, where it becomes very narrow, shallow and muddy. This would allow supplies to reach, say, Alloa, a possible bridging point of the Forth. The other major river under consideration is the Tay but as we have already seen, Carpow would have been reachable by even large vessels. Therefore were the river vessels used for transport to Alloa or somewhere else nearby in the upper reaches of the Forth, a process which would probably involve offloading the supplies at Cramond into the smaller river vessels or were they used as pontoons for Caracalla's bridge of boats as depicted in his coins? While the foregoing hypothesis of the motives for choosing the "coastal route" and the extensive programme of bridge building is to a degree speculative, it is not speculative in the absence of facts. Furthermore, I would submit that the policy of supplying the campaign by sea, though being an assertion with which undoubtedly many will disagree, fits better the more basic facts that have been accumulated over the past 30 or so years. A list of these facts are as follows:- 1) Line of 165 acre marching camps leading up the east coast towards Cramond. This size of camp is not continued further north than the Forth. It has been suggested that this indicates that part of the soldiery was taken by sea to various places in Fife but to me it seems more logical that it indicates the added space needed for the supply trains accompanying the army until it reached the next port at Cramond. 2) Decrease in the size of camps north of the Forth. As explained above. 3) Marshy ground described in Cassius Dio - emphasis on timber felling and road building. 4) Expansion of ports and granaries on the east coast. 5) The unprecedented size of the fleets in support of the military campaign. 6) Failure to garrison the lowlands of Scotland. 7) Lack of any sign of either re-use of prior camps or construction of new ones for the functioning of continual supply trains needed to support a field army of 30,000 men (or more). 8) Large numbers of smaller boats used i.e. lighters with flat bottoms from the Danube and Rhine areas. The foregoing details point to me to a concept of having a highly mobile, even if large, force which was not hampered by supply trains and which knew that it was never further than a couple of days march from direct access to resupply. It took a line of march up the east coast of England and Scotland precisely with this in mind and it was this concept which necessitated the building of the two bridges. The bridges ensured that their line of march kept relatively near the coast. Thus the reason for the massive effort in bridge building was strategic - it gave his forces a mobility freed from the need to mount a huge land based re-supply operation and the necessary garrisoning along the way that such a tactic would require. It also ensured that the enemy wasn't able to interdict his supplies as they were unable to come between the army and the fleet. This, I believe, is why Severus did not garrison the lowlands of Scotland, not as assumed by some writers, that he had no plan to stay in the long term. It may indeed be that he knew from the outset that he was not going to rout every single tribe that was restless under the Roman presence but I think there is ample evidence to suggest that he intended to deal such a decisive blow against the Caledonians that it would serve as a highly public demonstration and thus cow the others into submission and equally, that he intended to establish the new frontier of the Roman empire north of the Antonine Wall and keep it there.