They show its garrisoning units to have been as follows: The First Cohort of Frisiavones are also attested at Brocolitia at some stage, as shown by an inscription on an altar stone, which tells us that Optio Maus had repaid a vow to the goddess Coventina.

All three sites lie adjacent to a small tributary stream of Meggie's Dene Burn, which runs three miles from Carrawburgh to empty into the River South Tyne near Newbrough's fort on the Stanegate.

Nearest to the fort, about 80 metres (260 ft) from its south-west corner, are the remains of an early 3rd century mithraeum, i.e. a temple of the mystery cult of the Roman god Mithras.

Richmond and J.P. Gillam in 1950, it is the second-most northernly mithraeum discovered so far – only Bremenium (High Rochester), more than 10 miles (16 km) from Brocolitia, is further north.

[12]: 282 [13]: 77  Like most other mithraea, the Brocolitia temple was built to resemble a cave, and also had the usual anteroom, and a nave with raised benches (podia) along the sides.

The third stage includes three monuments by different cohort prefects, commanders of Cohors I Batavorum, a Roman Batavi unit of auxiliary cavalry stationed at Brocolitia.

Directly in front of the entrance to the mithraeum the remains of an apse, well, and altar were found and named as the Shrine to the Nymphs and Genius Loci, sometimes referred to as a "nymphaeum".

The altar, dedicated by M. Hispanius Modestinus c. AD 213, was inscribed identically on two sides, and stood on a pedestal indicating it was out in the open, and meant to be walked around.

It was built c.AD128-133, during the construction of the Vallum, in order to help control the water level of the area, it is likely after this it became associated with Coventina with the height of the cult being in the late 2nd to early 3rd centuries[15] when the Batavians were stationed at the fort.

Having been in private hands for many years, the fort, which is a scheduled monument,[16] was gifted to the nation in January 2020 by Jennifer Du Cane, whose family have owned the site since the 1950s.