In the largest field,can clearly be seen,the remains of the fort ramparts.The lesser bumps are remains of buildings within the fort.One major difference between this fort's structure and that of The Wall,was that the fort's ramparts were built of turfs.This tended to make a very wide rampart,which would slump over time,but was very quick to construct.Roman turves were 18ins.X 18ins.X 6ins.,and are easily identified in cross sections of ramparts.NB:Note how much higher the top of the ramprts are compared to the adjacent field.
see http://www.dur.ac.uk/resources/archaeological.services/research_training/hadrianswall_research_framework/project_documents/Birrens.pdf
see http://www.roman-britain.org/places/blatobulgium.htm