Complex sentence: Consuls were each assigned two of the four legions to command, rarely employing all four legions at once to the same assignment, however, the Senate feared a real threat and not only employed all four legions into the field, but all eight, including allies.
Split into simpler sentences: Consuls were each assigned two of the four legions to command, rarely employing all four legions at once to the same assignment. However, the Senate feared a real threat and not only employed all four legions into the field, but all eight, including allies.