When Caesar started his campaigns in Gaul his forces were close to full size: about 5000 men
each. After sometime the various legions were depleted through casualties, disease and service. Initially the legions might have been standard with each
legion having 10 cohorts which always was maintained. Each cohort on paper was composed of 3 maniples each of 200 men. The actual strength of a maniple would be about
120 at best but more like 60 men. This makes a cohort 360 men. In truth Caesar's legions were closer to 10 cohorts of 250 men each. About the same size as Alexander's
speria of pikemen. Both the speria and cohort, might be equated to a modern battalion. Battalions in more modern times were grouped together to make
regiments-2 or 3 battalions make a regiment. Caesar had 10 battalions to make a legion. This would be equal to a modern brigade. Perhaps each line
would be a regiment of sorts.Often Caesar does write about cohorts and not legions when assessing army strength.
As in earlier times the legion would deploy into three lines. Any skirmishers, would deploy on the flanks or directly in front of the first line. The velites were replaced with auxilia (not shown) of various nationalities. In this period (circa 100 B.C. to 100 A.D.) the legion did not distinguish between the old hastati, princeps and triarii. Now they were all armed identically with shield, sword, pila (throwing javelin), helmet and armor. For organizational reasons including seniority, the old titles but not the equipment were retained. The first line could deploy in close or loose order and consisted of 4 cohorts. The remaining two lines deployed to the rear and would consist of 3 cohorts each. Occasionally cohorts from the third line could be grouped as a fourth line.
Below are two legions deployed-scale of 1:100. In this instance each line is a single unit ignoring the actual cohorts as individual units. More on this later. On the left the legion is in loose order. On the right the legion is deployed in close order. Notice the frontage of both. From a distance an observer would think he is seeing a larger force than it really was. Shown here are two legions. One in close order (left) and one in loose order (right).