The Marching Camps and the Fort: First Phase – The Agricolan Fort
The earliest Roman remains on the site are a series (eight at the last count) of large marching camps (the ditches still visible after 2,000 years as dark lines in aerial photos). They represent temporary stopping places for tented armies on the march ie for the first garrison before they completed the fort or, after it was occupied, for visiting troops passing up or down the line, who could not be accommodated in the fort itself. They are of varying sizes, two being 40 and 50 acres in extent, and one being called by Curle ‘The Great Camp’. Trimontium may have been a gathering place for armies eg under the Emperor Septimius Severus in 208-10 when he campaigned in the North of Scotland and may have wintered at Cramond.
There are many periods or phases of fort construction at Trimontium. The first in 80 AD probably built by the Ninth Legion from York ( not ‘lost’, according to the latest evidence) during Agricola’s northern campaign leading up to his victory at Mons Graupius (in Aberdeenshire?) in 83 AD, was about 10.5 acres in extent, contained wooden buildings, and was defended by a rampart of earth only, built up on a foundation of cobbles, and with two V-shaped ditches, 9′ wide and 3′ deep approx, in front. In shape it was an ‘irregular’ fort in that it departed from the standard playing-card shape layout. The lines of the rampart in each quarter are staggered, so that people approaching the gates in each side must do so at an angle, thus exposing themselves to side fire. Other Agricolan forts in Scotland display similar characteristics, but the overall idea seems to be exceptional (the work of one engineer?) and examples are rare. See outline drawing. The West Annexe, an enclosure defended by two ditches, seems to have been the first extra-mural development.
It is suggested that the ala Petriana, the biggest in the country, provided the cavalry wing stationed at the fort at this time.
Second Phase – The Domitianic Fort (after the Emperor, Domitian)
About 86 AD the Agricolan fort was extended to 14.5 acres and its defences strengthened. The two ditches were infilled and replaced by a single huge ditch, 20′ across and 12′ deep. The earth rampart, again on a cobble and rubble base, was now 43 ‘ wide and 28’ high (including the palisade on top). The buildings, though still wooden, had stone foundations – to last longer. As with phase I, there is little evidence for the arrangement of buildings and streets within the fort.
First Abandonment or Gap in Occupation: Third Phase
The traditional view is that the first period of Roman occupation lasted from 80 to 105 AD. The Romans gave up trying to have a Tay-Forth or Clyde-Forth frontier line of forts. “In the early years of the second century the costs or risks of maintaining the outposts (in South Scotland) appear to have exceeded the advantages, and they were abandoned. For nearly forty years thereafter the lower isthmus (of the province of Britannia) formed the north-western frontier of the Empire, and the tribes of Scotland were left to pursue their respective ends without the hindrance or help of a resident garrison.” G S Maxwell, 1989.
The Emperor Hadrian’s visit to Britannia in 121-122 AD resulted in the building of the Hadrian’s Wall frontier. Again the traditional view is that Trimontium was re-occupied about 140AD and became a support centre to the rear of the (Forth-Clyde) Antonine Wall, when Hadrian’s successor Antoninus Pius brought an army back into Scotland. Trimontium may well have been re-occupied some time before that as an outpost fort, North of Hadrian’s Wall.
Re-occupation and Refurbishment: Fourth Phase – Outpost Fort
After twenty or even forty years’ absence the earth rampart immediately required an additional ‘dump’ of earth to strengthen it, and the fort ditches seem to have been hurriedly recut, with the inclusion of branches as an easily available additional deterrent. The buildings may have reverted to wooden construction in this ‘precarious’ phase. Extra-mural settlement, with a market place, existed in the South Annexe. There was capacity for 1,500 troops, not counting the South Annexe civilians. Like the initial first century Agricolan phase this second century re-establishment was probably brief.