Inchtuthil

In the summer of 1960 an excavation on the Tay opened a pit that had been elaborately hidden. Inside were 875,400 complete iron nails, from two inches long to sixteen, weighing about six and a half tonnes, along with cartwheel rims and other ironwork bringing the total to ten. The Romans put them there. When the legion dismantled this fortress and left, it buried its nails rather than leave the Caledonian tribes several tonnes of refined iron that could be forged into weapons.

That is the most famous thing about Inchtuthil, but it is not the most important one. The fortress was built in AD 82 or 83 as the advance headquarters for Gnaeus Julius Agricola’s campaign against the Caledonians, on a site at the head of one of the main routes in and out of the Highlands. It covered 21.5 hectares and held Legio XX Valeria Victrix — 5,400 men at full strength, with specialists besides. Two or three building seasons went into it, with a temporary camp alongside to shelter the soldiers through the winters while the work went on.

It did not stand alone. Smaller forts were placed north and south at the mouth of each nearby glen, the works now called the Glenblockers, and together with the Strathmore forts at Cardean and Stracathro and the road, forts and watchtowers of the Gask Ridge they formed a single system. Inchtuthil was its pivot, and the only base in it large enough to mount an invasion of the Highlands.

Inside the turf rampart, faced in stone with a ditch outside and a gatehouse on each of the four sides, were 64 barrack blocks, a hospital covering 5,000 square metres and a workshop covering 3,500. Somebody has worked out that the timber walls of those buildings amounted to seven miles of perimeter.

Two things in the plan do not fit. The headquarters building, with its aedes — the shrine holding the legion’s standards and the images of the emperor — is far smaller than a legionary fortress ought to have, and must have been a temporary arrangement. And the large plot immediately east of it, where the commander’s house belonged, is empty. The ground was levelled and prepared, and then nothing was built on it. The fortress was abandoned before its most important building was started.

The abandonment came around the summer of AD 86 and certainly no later than early 87 — four years or so after the first turf was cut. The reason appears to have had nothing to do with Scotland. Legio II Adiutrix was pulled from Chester to Moesia to meet a Dacian invasion in 86, and XX Valeria Victrix was obliged to move south and take its place. Recent archaeology has complicated that account, hinting the fortress may have been in use considerably longer than the traditional dates allow.

What followed the departure is the reason the site matters. Nowhere else did a legionary fortress escape being built over — the Roman fortresses of Britain became York, Chester, Caerleon, and their plans have to be recovered in fragments from beneath living cities. Inchtuthil was left in a field. When Sir Ian Richmond excavated it between 1952 and 1965 the layout was still largely intact, and it produced the only complete plan of a legionary fortress anywhere in the Roman empire.

The nails had an afterlife of their own. Many went to museums. Some were sold to the public and to interested organisations at five shillings for a nail of seven to ten inches, or twenty-five shillings for a boxed set of five. David Colville and Sons, iron and steel refiners, were given the job of sorting and storing them, and the sorting, gifting and selling of every complete nail was finished by 1963. Since then, atomic scientists have used the two-thousand-year-old iron to estimate how quickly barrels of nuclear waste will corrode — a use for a Roman legion’s leftovers that nobody could have anticipated in 1960, let alone in AD 86.