I think the primary secondary source for Imperial Era tactics is http://en.wikipedia.org/wiki/De_Re_Militari by Vegetius. As far as I know, the Chinese used shields of similar size to set up defensice positions that their halberd infantry fall back to and for their massed crossbowmen to fire from. Or that's how its interpreted in movies anyways :-p.

There is also modern riot police shield tactics if experimental archeology is your thing.