Quincunx and Keppie\'s hypothesis

[Cesco]

As for opening ranks, there was a number of methods. There would either be expansion of the phalanx or unit (to the left, to the right or to both flanks), or doubling (or multiplying) of the depth of files, in which case, the length of the phalanx remained the same. The doubling itself would take place either by whole files being posted behind the ones remaining in the front or by the men of the retreating file being inserted as epistatae/secundi within the file remaining in place. There is no reason to assume that the Romans, as the Greeks and others, did not use all these methods as circumstances demanded.

According to Maurice's Strategicon( I have found an italian traslation on the web ) the way to double the front ( reducing the ranks ) was the following ( and it is the same shown in the video I posted in the thread " Early republic consular army deployment"): the sixteen men constituting a file, or column, were divided in primi and secundi, that is uneven and even( the priores and posteriores of the maniple?). At the injunction " Exite! " the secundi left the column, going on the left or on the right. Before that the chief could have instructed to open the formation "Largia ad ambas partes!"