The location of the camp 15 miles out of Rome on the Via Appia was decided for a number of political reasons rather than strictly strategic. With the rise to the imperial throne of Septimius Severus after the rapid succession after Commodus of Elvio Pertinax and Didius Julianus, elected and killed by the Praetorian Guard, a new period started referred to by historians as the 'Severian Military Monarchy.' The disbanding of the Praetorians and the immediate re-formation of this select unit, this time with recruits drawn from all the legions of the empire, put an end to the Italian predominance within the fearsome Roman Army for ever. The quartering of the troops of the II Parthian Legion at Albano was ordered by the emperor on his return to Rome in April 202 after the campaign in the east against the Parthians. The three Parthian Legions were founded there in 197, two of which were destined to remain in the east, being given responsibility for garrisoning the newly instituted Province of Mesopotamia (199 A.D.) (Calderini p. 72) As it was forbidden under Roman law to garrision troops within the city of Rome, Septimius Severus circumvented this obstacle by basing the legion outside the city, his need being for a rapid reaction unit of unquestioned loyalty, ready to pacify the quick tempers of the urban soldiers. The legion was located on imperial property near the Domitian Villa. In a period when the standard building practices were more refined but also slower and costlier, the encampment was completed in a very short time by the soldiers themselves who were directed by the faber praefectus. Once the commandant had chosen the site for the camp the castramensori traced the lines of the streets, measured the rectangular spaces for the individual cohorts and indicated the lines of the external walls. Each legionaire knew exactly where to put his tent, dig the fossato and to build his portion of wall, in what was a collective operation brought to completion through the precise subdivision of tasks. In plan view the camp formed an irregular rectangle with 1.334 ml of fortified walls surrounding it. The inclination of the camp with respect to the Via Appia was due to the necessity to use the pre-existing terracing of the Domitian Gardens that made best use of the gradient of the terrain. The blocks of peperino quarried and dressed on site, have various dimensions; length between 1 and 3 metres, height from 57 to 76 cm., thickness 90 cm. Circular towers were built in the two corners nearest the Via Appia, and rectangular signalling and defensive towers were built along the sides. The entrances were positioned in accordance with the normal military plans for fortified camps. The Praetorian Gate was constructed with three arches on a gigantic scale measuring 36 m long and facing the Via Appia. The 'Via Praetoria' connected the praetorium and the Praetorian Gate. The two main gates opened, instead, on the larger sides and were joined by the 'via principalis.' The walls measured 435m on the northwestern side and 232m on the southeastern side enclosing more than 10 hectares of land. The stone used in the construction of the walls, peperino, was quarried on site and thus the material was put to use as soon as it was extracted. The blocks were raised and positioned by the ferrei forficies (metal tongs of large dimension designed for the handling of huge blocks of stone), while at the same time the plans for the inner construction work were drawn up. The chapel of the patronal divinity had a privileged position near the commandant's quarters (praetorium), and in it the the eagles and other consecrated military emblems were kept (Forni p.844 Calderini p. 326). The military camp of Albano never had the physically dominating aspect equal to other front line camps scattered throughout the empire. In fact the choice of site demonstrates a certain incompatibility with some of the basic principles of fortification contained in the relevant military manual of the time the castramentatio. "Placed on a hilltop........ isolated from all other buildings and from dangerous places." From the crest of the present day Colle dei Cappuccini (hill of the Cappuccini) the camp of the II Parthian Legion was completely visible and vulnerable even from personal weapons, to say nothing of heavy weapons like the ballistae lanciadardi. This 'weakness' was accentuated by the construction of the amphitheatre and the baths; the baths being structurally connected to the camp by an acquaduct which in the case of attack would have been an easy means of penetrating into the camp. Thus it is clear that the legion with its six thousand men at arms had a quite different function from the traditional one. In fact it was progressively furnished with the same privileges and services as were given to the urban soldiers of Rome and the Praetorian cohorts. After the death of Septimius Severus the influence of the legion at Albano gradually grew until becoming a political deterrent and influence over the emperors themselves, deciding their fate and often their life. The sources report the presence of the II Parthian Legion in the imperial retinue throughout the 3rd cent. but only as detachments attached to other legions, like support troops or a rapid reaction force. It is certain that some cohorts remained to garrison the camp at Albano, maintaining the function of military police in the city and in the imperial domains. The departure of the legion and the abbandonment of the camp is mentioned in the Liber Pontificalis, as due to the Emperor Constantine.. In the months that followed his entry into Rome and his election by the Senate as primus augustus, Constantine took some important decisions in the reordering of the administration and the State; he appointed consuls, disbanded completely the decimated Praetorian cohorts and the urban militias loyal to Massenzio (Levi p. 554) and had the fortified camps dismantled, transferring their great military structures to civil use. It could be precisely for this reason that the II Parthian Legion was forced to leave the by now populous urban centre of Albano, and head towards other provinces of the empire (to Mesopotamia and in northeast Macedonia where it was employed along with the III Augusta). Thus all the events point to a precise aim on the part of Constantine, to demilitarize the urban and suburban areas, which had by ths time already lost their politico-military pre-eminence in a process which had been gathering speed from the beginning of the 3rd cent. right up to the end of the Western Empire. Through Constantine the military camp, the service structures, le canabae which had been transformed by the legionaries and their families into regular normal places of habitation, now became an integral part of the the town (Galieti p.31). In the space of a few years the inside of the camp was swallowed up and incorporated into urban dwellings while at the same time materials were systematically re-utilised in new structures, a process which was to be the fate of all imperial constructions. This process was to continue right up till the 18th century and was especially great between the 12th and the 18th cent where the imperial structures were used as a base for new grand constructions. Thus these ravages, while largely wiping out the military nature of the original site, allow us to see, through the fabric of the subsequent civil building, the entire story of the genesis of the site and the later development, strongly influenced by the extraordinary powerful presence of the the Castra.