The Legion in the American Civil War was a roughly regimental sized combined arms unit with companies of infantry, cavalry and artillery. They were Intended to be a self-contained miniature army. Both sides experimented with legions in the early days of the war.

As the sizes of the armies grew It became apparent that operating a combined arms unit of such a small size was inefficient. As time went on they were almost all broken up. Their infantry was increased to regimental strength, their artillery companies became independent batteries, and their cavalry companies became independent or were incorporated into existing cavalry regiments or battalions. Sometimes the name “Legion” continued to be used for parts of the original organization after the units were broken up.

Examples:

Purnell Legion (Maryland-USA)

Broken up in into the Purnell Legion Infantry, a regiment of nine companies of infantry; Purnell Legion Cavalry, Companies A & B, two independent companies of cavalry; and Battery A and Battery B, Maryland Light Artillery, two independent batteries.

Hampton Legion (South Carolina)

Organized with six companies of infantry, two companies of cavalry and a company of artillery. The infantry was reorganized as a regiment but retained the name “Hampton Legion Infantry“. The cavalry companies were combined with a third to become the Hampton Legion Cavalry Battalion. This was then combined with two other cavalry companies to form the 2nd South Carolina Cavalry Regiment. The artillery company became an independent horse artillery battery, the Washington Artillery, or Hart’s Battery.

10th New York Legion

Originally organized with eleven companies of infantry, two companies of cavalry and two batteries of artillery. It was broken up before it mustered into Federal service. The infantry became the 56th New York Infantry Regiment, the artillery became the 7th and 8th New York Independent Batteries, and the cavalry became part of the 1st New York Mounted Rifles.

Legions in Name Only

A number of units were sometimes referred to as legions but were legions in name only for recruiting and public relations. They never had the combined arms structure of an actual legion, even when first formed.

Examples:

58th New York Infantry Regiment (“Polish Legion”)