[citation needed] The site of the Flavian (1st century) fort lies 1 km to the west of the modern town of Dalkeith, south-east of Edinburgh.

Extensive examination of the annexe highlights the ancillary, probably military, character of the activities taking place there and emphasises, in contrast with the fort, substantive changes in use over a relatively short time-span.

Thus it served as a garrison post (castellum) as part of the more permanent consolidation of Roman control in Scotland during and immediately after the campaigns of Gnaeus Julius Agricola.

There is also unique evidence that the site continued to function as a collection centre for animals after the garrison had departed: the interior of the fort was cobbled over, two additional wells were dug and ditches inserted across the annexe to funnel livestock.

The Elginhaugh coin hoard is a group of 45 denarii which provides the terminus post quem dating of AD 77-78 for the construction of the fort and was argued by the excavators to represent a foundation deposit for the Principia.