The term Medieval does not have a strict historical definition, and in relation to the setting of romance novels can cover a large period of time. Generally Medieval romances are set between 938 - 1485 AD. Books set before that time are considered to be about the Dark Ages which is defined as between 402 - 937. The definition of these time periods will depend upon the location of the events in the novel. Events in England which typically are referenced are the Norman Conquest (1050-1120) including the Battle of Hastings in 1066 when William of Normandy killed King Harold and the crusades which occurred from 1096 to 1270.
For books set in the medieval period, see Category:Medieval.