Lances and horsemen were involved in fighting since the dawn of history, and plate armor hails from 13th century (if we follow rather loose definition, and say that coats of plates, or single plates here and there count as "plate armor).
In crusade records I mentioned, we can only assume that "lorica" or some other latin word from sources refers to mail, because it was most prized form of armor among Europeans back then.
Five pound warhammer would be two handed one, one handed is rather unlikely.We are talking, if I understand correctly, about the difference between 3-pound swords and 5-pound hammers. Five pounds may not sound like much compared to the way D&D weighs weapons, but stuck on the end of a long stick it can be quite awkward (especially compared to maneuvering around with a sword).
http://wallacelive.wallacecollection...ype=detailView
http://wallacelive.wallacecollection...ype=detailView