We know of at least eight different auxiliary units who served on the Wall from countries as far off as Syria. Auxiliaries were men drawn into the army from across the Roman empire, sometimes voluntarily, sometimes by force. Once the Wall was completed it was garrisoned mainly by auxiliary troops, with small detachments from the legions.
The Wall was built mostly by men from three different military ‘legions’, career soldiers who had committed to the army for a period of twenty-five years. This was about the same number who defended Hadrian’s Wall, twice the length of the Antonine Wall.