Gariannonum (also written Garianonum, Gariannum) is a Roman fort near the village of Burgh Castle in Norfolk, one of several Roman forts that were built as a defence against Saxon raids up the rivers of the east and south coasts of southern Britain (the Saxon Shore). Established between 260 and the mid-270s to guard the River Yare (Gariannus Fluvius), it was garrisoned by the Equites Stablesiani Gariannoneses, a detachment of the elite troops of the Stablesian auxiliary cavalry. six miles north east is another Roman fort at Caister-on-Sea.
The ruins of the fort are in the care of English Heritage. Unlike most Roman ruins in Britain, the walls and buttresses still exist above ground level. Access is free and unrestricted.