A Roman fort at Hadrian’s wall, in Northumberland, built around 122AD and which housed a garrison of 500 soldiers from Gaul, has been given to the nation.

English Heritage has announced that Carrawburgh Roman fort has joined sites such as Stonehenge, Tintagel castle, and Eltham palace, in the national collection of historic sites and properties following its gift by a landowner.

Carrawburgh is one of 16 forts along Hadrian’s wall, a boundary line that stretches 73 miles. It accommodated soldiers, first from the south-west of France and later southern Belgium, as part of the Roman effort to defend the imperial frontier and repel tribes from the north.

The fort sits between the Roman cavalry fort at Chesters and the infantry outpost at Housesteads. Nearby is a Roman temple built by the fort’s soldiers and dedicated to Mithras, an eastern god who, according to legend, captured and killed the primeval bull in a cave.

Today sheep are more likely to be grazing on the grassy mounds which largely cover the remains of the 1.4 hectare (three and a half acre) fort. English Heritage said that compared to other sites on the wall Carrawburgh had undergone very little archaeological excavation, which meant it had many secrets and stories to be explored.

The site has been looked after by the family of Jennifer Du Cane since 1950. She said: “It has been a great privilege but also a serious responsibility to own Carrawburgh Roman fort. The time has come to pass on this amazing site as a gift to the nation.”

Facebook Twitter Pinterest Carrawburgh Roman fort, one of 16 along Hadrian’s wall. Photograph: Justin Minns/English Heritage/PA

Carrawburgh is the first site of its type acquired by English Heritage since the body was made a charity by the government in 2015.

Kate Mavor, English Heritage’s chief executive, said: “This is a great start to the new year, not only for English Heritage but for the nation who will get to enjoy this wonderfully evocative site on what was once the edge of the Roman empire.”

Legal ownership of the site has transferred to Historic England, the government’s heritage adviser, and it will be cared for by English Heritage as part of the national heritage collection, which comprises about 420 sites, many free to enter, that together tell the story of England.

Duncan Wilson, chief executive of Historic England, said: “We are enormously grateful for this generous gift. Hadrian’s wall is one of England’s most important historic sites and Carrawburgh makes a really valuable addition to our national collection of historic properties.

“The fort represents a key part of the Roman frontier and is of outstanding archaeological significance. It has the potential to contribute significantly to our knowledge of the Roman empire and to visitor enjoyment of the wall.”