The early Roman army (c. 500 BC) was a citizen militia
It was small
Organized in five classes
Three providing hoplites and two providing light infantry
The early Roman army was tactically limited and its stance during this period was essentially defensive.
After this Military Strategy did not work, they switched to a Legion
The early Republican legion consisted of five sections
Each of which was equipped differently and had different places in formation:
Three lines of manipular heavy infantry hastati, principes, triarii
A force of light infantry velities
The cavalry equites
At nominal full strength, an early Republican legion included 4,000 to 5,000 men: 3,600 to 4,800 heavy infantry, several hundred light infantry, and several hundred cavalrymen.