Models in a unit of infantry or cavalry are arranged in a formation that consists of one, two, three or more horizontal lines, called ranks (See Diagram 6.1 - Ranks & Files). As far as possible, the unit always has the same number of models in each rank and, where not possible, it is always the rear rank that is left short (in which case it's referred to as an incomplete rank). The last rank is filled from the centre. The vertical lines of models in a unit are called files, and that explains why sometimes the members of a unit are referred to as 'the rank-and-file troopers' (to distinguish them from characters that have joined the unit).