That alone would make it interesting. What makes it remarkable is what has been turning up in the soil: Roman coins from the second century AD, fibulae of Romano-British type (decorative brooches used across the Roman world), copper ingots, Gallo-Roman pottery, and nearly eighty sherds of Dressel 20 amphorae, the distinctive round-bottomed storage vessels used to ship olive oil from the Roman province of Baetica in what is now southern Spain. Ireland was never part of the Roman Empire, and yet Drumanagh appears to have been in sustained contact with it.

The fort's landward defences consist of three earthen banks, each originally fronted by a ditch, with traces of a fourth outer bank beyond the last ditch. The inner bank is the best preserved, measuring around 30 metres wide and 2 metres high, while the outer banks have been considerably worn down. A small stream feeds along the inner ditch and drops over the cliff at the south-west corner of the headland. A Martello tower, one of a chain of coastal watch-towers built around 1804 during the Napoleonic Wars, stands at the eastern end, and its original approach road survives as a sunken trackway running from the south-east corner of the fort. The site has been under a preservation order since 1977, though that has not prevented damage: ploughing in the 1970s exposed hut sites, and further ploughing in 2014 cut into the outer bank and a large oval enclosure identified just outside the ramparts. Geophysical survey and LiDAR analysis have since revealed a D-shaped enclosure and several structures inside the fort, while that external oval enclosure, roughly 42 metres east to west, may have its own original entrances on its north-east and south-east sides.

Three seasons of community excavation organised by Fingal County Council under the Digging Drumanagh project have added considerably to the picture. Work in 2018 near the Martello road uncovered Iron Age deposits disturbed by its construction, along with fragments of human bone including a cranial fragment from a woman aged between 18 and 45, dated to between 170 BC and AD 52. The 2019 season, working closer to the ramparts, found post and stakeholes from a prehistoric structure alongside a weaving comb, bone points, and a bone needle, suggesting textile production was taking place here. The 2022 season recovered sherds from at least four types of Roman pottery, glass vessel fragments, and glass beads. The site remains under active investigation, and a 3D model is available online at skfb.ly/oEQ7n for those who want to explore the earthworks before or instead of a visit to the headland itself.