Historia regum Britanniae (The History of the Kings of Britain), originally called De gestis Britonum (On the Deeds of the Britons), is a pseudohistorical account of British history, written around 1136 by Geoffrey of Monmouth. It chronicles the lives of the kings of the Britons over the course of two thousand years, beginning with the Trojans founding the British nation and continuing until the Anglo-Saxons assumed control of much of Britain around the 7th century. It is one of the central pieces of the Matter of Britain.
Although taken as historical well into the 16th century, it is now considered to have no value as history. When events described, such as Julius Caesar’s invasions of Britain, can be corroborated from contemporary histories, Geoffrey’s account can be seen to be wildly inaccurate. It remains, however, a valuable piece of medieval literature, which contains the earliest known version of the story of King Lear and his three daughters, and helped popularise the legend of King Arthur.