heavy cavalry engaging heavy cavalry

[Dan Howard]

Assyrians are sometimes credited with developing first true heavy cavalry formations.

As far as I can tell there was no heavy cavalry employed by anyone that early. Even their chariotry didn't operate as heavy units. It isn't until the reforms of Cyrus that chariots operate like true heavy units and heavy cavalry doesn't appear until even later. The Assyrians are likely to have been the first to employ horse archery in the region though.