Hill cloud rolls over the fell top where snow still fills the cups and hollows of high ground. I’m walking a section of the Pennine Way near Alston, uplifted by the layers of overlapping sound: curlews bubbling, peewits wing-thrumming, skylarks trilling. The path drops steeply down to the Gilderdale Burn, the county boundary between Cumbria and Northumberland. Climbing up again, the ground is spongy with recent rain, wet seeping into my boots.

A series of grassy mounds and banks stand lime-green vivid against a lowering sky. Tiered like contemporary landform art, they were made nearly 2,000 years ago. This is Epiacum Roman fort on Castle Nook farm, and it has some of the best preserved earthworks of Roman Britain. Built about the same time as Hadrian’s Wall to the north, it is on the line of the Maiden Way that marched up to Carvoran. Archaeologists believe its purpose was to control lead and silver mining. The standard Roman rectangular fort is here skewed into a lozenge shape to fit the slope of the hill.

Although not the highest point, the fort commands the South Tyne valley with its river looping along the bottom. A drystone wall undulates over rows of corrugated ramparts, a series of banks and ditches where rushes grow in the wet places. Under the yarrow and sheep’s sorrel of the short turf were the gateways, towers, barracks, granary and bath house of the stone-built fort. Now, a pair of ravens croak as they circle and swoop in tandem, linked on invisible strings.

The Pennine Way near Alston. Photograph: Susie White

In 1825, a farmer spread the rich “manure” of the Roman rubbish dump across the fields, digging up leather shoes, pottery and a battle axe. There were small excavations in 1810 and 1957, but archaeology now is non-invasive using lidar or recording objects found in molehills: a jet bead, a decorative bronze dolphin. Until last September, a 19th-century dry-stone wall cut a V-shaped wedge across the fort. As the wall was taken down, buried within were Roman artefacts: broken quern stones, a roof tile, a column base, the neck of an amphora, a dusky blue fragment of glass, signs of a life lived on this high fell where sheep graze and wading birds call.