Complex sentence: Founded around A.D.90, probably to house an Auxiliary cohort of around 500 men, it was drastically altered when a second fort was built in stone over its eastern defenses around A.D.120; effectively leaving a western annex of about 0.8ha.
Split into simpler sentences: Founded around A.D.90, probably to house an Auxiliary cohort of around 500 men. It was drastically altered when a second fort was built in stone over its eastern defenses around A.D.120; effectively leaving a western annex of about 0.8ha.