Quote Originally Posted by Thaatu
1.) Didn't hypaspists fight on the right flank of the battle line, as the right hand of the phalanx? If so I would say they needed more armour against phalanx armies. Could be wrong though...
Most sources I've seen agree on if nothing else on the hypaspists, or in any case Philip's and Alex's original ones, to have acted as a mobile "link" between the pike line and the Hetairoi. Sort of as backup for the cavalry, to prevent an unacceptable disjointing of the line as the horsemen inevitably outpaced the pikemen and, presumably, elite flankers who started rolling up the enemy line from the side once the Hetairoi had punched thrhough.

Anyway, the big limiter on phalangite mobility was the need to mainatin formation integrity without which the sarissae were next to worthless for most purposes. The Hypas were presumably either armed with something else - "hoplite" type weapons loadout would seem sensible - not requiring quite as rigid maintenance of ranks or so much better drilled they could be more maneuverable than the grunts. In either case they should've been able to wear anything up to bronze plate and still be more agile than the rank-and-file pike units; it's not like that armour is so heavy anyway, especially for elite soldiers.

Dunno how exactly the Successors used theirs though.