Complex sentence: The exact size of the unit, which was at least partially mounted, is also unknown, but is referred to as a cohort, which in this period normally implied; it could have had a strength under the Emperor Caligula of 500 to 1,000 men.
Split into simpler sentences: The exact size of the unit, which was at least partially mounted, is also unknown, but is described in ancient sources as a cohort, which in this period normally implied a strength of ca. It could have had a strength under the Emperor Caligula of 500 to 1,000 men.