Henry's control of Normandy was challenged by Louis VI of France, Baldwin VII of Flanders and Fulk V of Anjou, who promoted the rival claims of Robert's son, William Clito, and supported a major rebellion in the Duchy between 1116 and 1119.

[2] These Anglo-Norman barons typically had close links to the Kingdom of France, which was then a loose collection of counties and smaller polities, only nominally under control of the king.

Physically he resembled his older brothers Robert Curthose, Richard and William Rufus, being, as historian David Carpenter describes, "short, stocky and barrel-chested," with black hair.

[18][nb 4] William's funeral at Caen was marred by angry complaints from a local man, and Henry may have been responsible for resolving the dispute by buying off the protester with silver.

[21] The two brothers disagreed fundamentally over the inheritance, and Robert soon began to plan an invasion of England to seize the kingdom, helped by a rebellion by some of the leading nobles against William Rufus.

[27] This also gave Henry influence over two major Norman leaders, Hugh d'Avranches and Richard de Redvers, and the abbey of Mont Saint-Michel, whose lands spread out further across the Duchy.

[55] The events of the final days of the siege are unclear: the besiegers had begun to argue about the future strategy for the campaign, but Henry then abandoned Mont Saint-Michel, probably as part of a negotiated surrender.

[57] Henry's next steps are not well documented; one chronicler, Orderic Vitalis, suggests that he travelled in the French Vexin, along the Normandy border, for over a year with a small band of followers.

[73][nb 9] Chaos broke out, and Tirel fled the scene for France, either because he had shot the fatal arrow, or because he had been incorrectly accused and feared that he would be made a scapegoat for the King's death.

[98][nb 12] Following the birth of these children, Matilda preferred to remain based in Westminster while Henry travelled across England and Normandy, either for religious reasons or because she enjoyed being involved in the machinery of royal governance.

[105] In February, Flambard escaped from the Tower of London and crossed the Channel to Normandy, where he injected fresh direction and energy to Robert's attempts to mobilise an invasion force.

[109] With the invasion imminent, Henry mobilised his forces and fleet outside Pevensey, close to Robert's anticipated landing site, training some of them personally in how to counter cavalry charges.

[124] He arranged the marriages of his illegitimate daughters, Juliane and Matilda, to Eustace of Breteuil and Rotrou III, Count of Perche, respectively, the latter union securing the Norman border.

[141] Henry's reserves, led by Elias I, Count of Maine, and Alan IV, Duke of Brittany, attacked the enemy's flanks, routing first Bellême's troops and then the bulk of the ducal forces.

[148] Henry inherited the kingdom of England from William Rufus, giving him a claim of suzerainty over Wales and Scotland, and acquired the Duchy of Normandy, a complex entity with troubled borders.

[154] Political friendships, termed amicitia in Latin, were important during the 12th century, and Henry maintained a wide range of these, mediating between his friends in factions across his realm when necessary, and rewarding those who were loyal to him.

[157] Over time, he increased the degree of his control over the barons, removing his enemies and bolstering his friends until the "reconstructed baronage", as historian Warren Hollister describes it, was predominantly loyal and dependent on the King.

[161] The familia regis included Henry's mounted household troops, up to several hundred strong, who came from a wider range of social backgrounds, and could be deployed across England and Normandy as required.

[163] Henry's court was grand and ostentatious, financing the construction of large new buildings and castles with a range of precious gifts on display, including his private menagerie of exotic animals, which he kept at Woodstock Palace.

[187] A distinction was drawn between the secular and ecclesiastical powers of the prelates, under which Henry gave up his right to invest his clergy, but retained the custom of requiring them to come and do homage for the temporalities, the landed properties they held in England.

[195] Henry increasingly drew on a wider range of these bishops as advisors – particularly Roger of Salisbury – breaking with the earlier tradition of relying primarily on the Archbishop of Canterbury.

[197] This stability shifted slightly after 1125, when he began to inject a wider range of candidates into the senior positions of the Church, often with more reformist views, and the impact of this generation would be felt in the years after Henry's death.

[205] He also focused effort on promoting the conversion of communities of clerks into Augustinian canons, the foundation of leper hospitals, expanding the provision of nunneries, and the charismatic orders of the Savigniacs and Tironensians.

[233] Henry crossed into Normandy in 1115 and assembled the Norman barons to swear loyalty; he also almost successfully negotiated a settlement with Louis, affirming William's right to the Duchy in exchange for a large sum of money.

[259] Henry had left the port of Barfleur for England in the early evening, leaving William Adelin and many of the younger members of the court to follow on that night in a separate vessel, the White Ship.

[267] The White Ship disaster initiated fresh conflict in Wales, where the drowning of Richard, Earl of Chester, encouraged a rebellion led by Maredudd ap Bleddyn.

[287][nb 31] Putting forward a woman as a potential heir in this way was unusual: opposition to Matilda continued to exist within the English court, and Louis was vehemently opposed to her candidacy.

[304] A fresh rebellion broke out among the barons in southern Normandy, led by William III, Count of Ponthieu, whereupon Geoffrey and Matilda intervened in support of the rebels.

[309] The King died on 1 December 1135, and his corpse was taken to Rouen accompanied by the barons, where it was embalmed; his entrails were buried locally at the priory of Notre-Dame du Pré, and the preserved body was taken on to England, where it was interred at Reading Abbey.

[323] Modern histories of Henry commenced with Richard Southern's work in the early 1960s, followed by extensive research during the rest of the 20th century into a wide variety of themes from his reign in England, and a much more limited number of studies of his rule in Normandy.