Henry I was the fourth son of William I (the Conqueror), and succeeded his brother William II to the English throne in 1100 at the expense of the eldest son, Robert Curthose, who was away on the First Crusade at the time. The following year Robert invaded to claim the crown for himself, but was temporarily pacified through the Treaty of Alton, whereby Henry agreed to pay him an annual sum of 30,000 marks to return to Normandy. In 1106 Henry decided to eliminate any threat from Robert by invading Normandy himself. The ultimately decisive battle took place on 28th September, almost exactly 40 years after their father's conquest of England in the Battle of Hastings. Robert's defeat made Henry not only King of England but also Duke of …
Editors. "Reign of King Henry I". The Literary Encyclopedia. First published 31 July 2012; last revised 30 November -1.
[http://www.litencyc.com/php/stopics.php?rec=true&UID=632, accessed 28 April 2015.]