The most basic infantry building block was the infantry regiment (referred to as a “battalion” in Hardee’s drill manual, which was used by both sides). In both North and South the infantry regiments were organised on similar lines.
A regiment typically comprised ten companies, each numbering 100 men, supported by staff, drummers and officers. However, the rigours of warfare would summarily lead to a reduction in strength by way of battle, disease and desertion, and a regiment's numbers could vary wildly.
Unlike the North, the general policy of the Confederacy was to send raw recruits to reinforce existing regiments in an effort to keep them at fighting strength. This also bestowed the recruits with the benefit of learning from more experienced fighters.