[split] Distances between files and ranks

[Bryan]

Metellus maneuvered his army to triplex acies battle array, with skirmishes between maniples, to counter the threat on the right flank.

That sounds right - and the map looks good too!

The only thing I don't get is why he brought up three lines of reserves to strengthen his flank - he'd only need two extra to form the triplex acies. Unless one of the lines was made up of skirmishers, perhaps on the extreme right? Or is there another explanation?

Its a kind of confusing battle description. It seems like Sallust is describing a formation of triplex acies but maybe not. He starts off by mentioning maniples (specifically in reference to placing skirmishers in between the gaps), but halfway through the battle he starts referring to cohorts for the first time referencing Romans and not Socii, which is why most modern historians when describing the evolution of the manipular legion to cohortal generally start with 109 BC. 

After re-reading the source numerous times to try to get a feel for what happened, I think the main body (as it could only apply to them, not Rutulius Rufus' advanced wing) had three lines of infantry in column, probably in double files in order to close up the width of the marching column, and were flanked on the right with either skirmishers or cavalry, who changed positions once they entered the plain. Either way, I can see Metellus' army stopping and shifting again when it became obvious that Jugurtha had closed off the entrance to the plain, and when Jugurtha's forces descended the ridge and entered the plain themselves. At that point the battle would have been imminent, while at the same time Metellus needed to reach the river for safety. With much more room to maneuver, he could have quickly shifted all the lines into deeper formations to be ready for the eventual Numidian attack.