Royal Commission aerial reconnaissance on 9th July 2018, during the 2018 drought, recorded Castell Allt-goch hillfort (NPRN 303882) under severely parched conditions. A surprise discovery immediately to the south of the fort, and built directly adjacent to the Iron Age defences, was a narrow-ditched square enclosure with rounded corners measuring 62m square. This had the character of a small Roman camp. It was built into the southern terminals of the outworks of the Iron Age hillfort, and appears to have built over or slighted one of the innermost ditches. 

Welsh Government LiDAR data from 2023 adds further detail. This shows the denuded earthworks of the camp, displaying characteristic broad earthworks with lower-lying central sections - implying the sites of gateways. A combination of LiDAR evidence and the parchmarks also suggests the presence of an external titulum bank on the south-west side, confirming a Roman date.

The unusual presence of a Roman camp built alongside - and into - the outer defences of a hillfort, appears to be a first for Roman Wales. Whether the camp results from an active military campaign or whether, as seems more likely, it was built for training purposes, cannot be answered from aerial photography alone.

T. Driver, RCAHMW, 2023