A file is a military term for a number of troops drawn up in line ahead, i.e. one behind the other in a column. The number of files is the measure of the width of a formation of troops in several ranks one behind the other.
Ancient Greek use
A file of men in the Greek phalanx was called a lochos (Greek: λόχος) and usually ranged from 8 to 16 men.
The original article can be found at File (formation) and the edit history here.