What Was the Council of Chalcedon Really About?

Clean Cut: Episode Directory
nameunderheaven...
Clean Cut; Episode 571
Did any new heresies need to be dealt with at Chalcedon? Has there ever been a fake council? What issues were dealt with at the council of Chalcedon?
All well-reasoned comments welcome.
If you're new to the series, I hope you'll check out the previous episodes, as they contain a lot of deductions, which I'll be building on.