When we needed Napoleonic zombies (for Pride and Prejudice) we used Mantic ghouls and added ragged tissue paper clothing (including kilts - we had Scottish zombies) - tissue paper soaked in glue to harden it - and spare Victrix pieces (mostly weapons but also some heads and shakos).
I would guess the same would work for ancient zombies if you add helmets, shields, etc.
They didn't look too bad and it gave us a lot of zombie figures for a reasonable price.
In the game the Scottish zombies moved faster (we justified it as "because they wear kilts" they don't just shuffle along)- intimidated the players trying to escape from them.