Dark Ages: Vampire Revised
From VTR
Dark Ages: Vampire Revised (as opposed to Vampire: The Dark Ages) was published in 2002 and contains revised rules and settings for a Dark Ages game of Vampire: The Masquerade.
For this game's purposes this is the book which contains the basic setting information for the dark ages period of the game. Also, it is the source for rulings that are not present in the V20 book, such as the rules for the Ride ability.