From "Debrett's Kings and Queens of Britain" by David Williamson, ISBN 0-86350-101-X, p. 69-70:
Acceded 19 Oct 1216
Crowned Gloucester Cathedral 28 Oct 1216 and again at Westminster Abbey 17 May 1220
The throne of England was occupied by a child for the first time since before the Conquest. Queen Isabella and her children were residing at Gloucester when John died, and , since the greater part of eastern England was in the hands of Louis of France and the rebel barons, it was thought expedient to have the 9 year old Henry crowned as soon as possible. Since the regalia was at Westminster and therefore not available, and John's personal state crown had been lost in the Wash, the young King was crowned in Gloucester Cathedral by the Bishop of Winchester with a gold torque (or bracelet, according to some accounts) belonging to his mother. The regency was exercised by William Marshal, Earl of Pembroke, until his death in 1219 then by Hubert de Burgh. The King's person and education ( his mother having retired to her native land at the first opportunity and remarried) were entrusted to Peter des Roches, Bishop of Winchester. Hubert and the Bishop were soon to become deadly rivals. The French invaders were expelled and the rebel barons brought to heel by the end of 1217 and on Whitsunday 1220 Henry was crowned for a 2d time in Westminster Abbey with the full ceremonial.
In order to secure the resumption of the royal castles and demesnes which had passed into private hands during the recent civil war, Henry was formally declared of age by Pope Honorious in 1223, but his personal rule did not commence until 1227 when he was 20. Even then, Hubert de Burgh retained a great influence until Jul 1232 when he was dismissed as Justiciar, accused of filling his own pockets from the royal treasury and other malpractices, and imprisoned. Although he was probably guilty of some of these charges, the King was really using him as a scapegoat for the failure of his own ineffectual expedition to France to recover some of the Continental possessions lost by John. Peter des Roches, who had prudently left the kingdom on the declaration of Henry's majority, now returned to power and appointed his fellow Poitevins to high offices, initiating the long period of bad government for which the weak-willed Henry's reign is best known.
When the barons, headed by Edmund Rich, Archbishop of Canterbury, finally demanded the expulsion of the Poitevins in 1234, Henry assumed the administration himself, filling the high offices of state with his own men. His extortionate taxation, disastrous foreign policy, and the favoritism shown to his wife's foreign relations and his own half-brothers, brought matters to a head and the lay barons of the kingdom found a leader in the person of Henry's brother-in-law Simon de Montfort, Earl of Leicester.
In the ensuing civil war Henry and his son Edward were defeated and captured by de Montfort at Lewes in 1264 and the King was forced to summon a parliament and undertake to rule with the advice of a council of barons. While the King submitted 'the Lord Edward' continued to lead the opposition and Montfort was killed at Evesham in 1265. Thereafter Edward and Henry's brother, Richard of Cornwall, concluded a peace with the remaining rebels.
For the rest of his life, Henry was but a cipher and the forced inactivity eventually resulted in premature senility. The death of his beloved brother Richard was a mortal blow. While praying at St Edmund's shrine in Suffolk, Henry "began to wax somewhat crasie' in the words of Holinshed. He recovered enough to call a council there, but suffered a relapse and was taken with all speed to London, where he died at the Palace of Westminster.
He was 65, and had reigned for 56 years. By his own directions he was interred in the original coffin of Edward the Confessor, who had been reburied in a more magnificent one, having with his usual simplicity an idea that its previous occupation by the royal saint had made it a peculiarly desirable tenement.
If Henry was a bad king, he was not a bad man, possessing none of his father's viciousness. The troubled realm he inherited would have needed a very strong ruler indeed to restore stability. Henry was not the man for the job and it remained for his far abler son and brother to accomplish it. What he lacked in statesmanship was largely compensated by a cultivated mind and a patronage of literature and the arts which had been neglected by his immediate predecessors. His rebuilding of Westminster Abbey, atributed to his profound veneration for Edward the Confessor, whose relics he personally assisted in carrying to their new shrine on 13 Oct 1269, was his greatest achievement and it stands today. Henry was the first sovereign to use a distinguishing numeral on some of his coins, the inscription oh his silver pennies reading "Henricus Tertius."