The custody of the Tower was committed by the Conqueror to a Constable or Governor, whose office was at first hereditary. In or about the year 1140 it was held by Geoffrey, grandson of Geoffrey de Mandeville, who was created Earl of Essex by King Stephen. Soon afterwards he took the side of the Empress Maud, and being besieged by the citizens, sustained the attack for a long time, and in a sally took the Bishop of London prisoner at Fulham. The Tower seems to have been regarded in those days as impregnable, and Geoffrey retained his possession of it until 1143, when he was taken prisoner by stratagem, and compelled to surrender it. The possession of the Tower fortress was always regarded by the English monarchs as of the highest importance, as it enabled them to overawe the citizens, and also furnished a safe retreat for the sovereign's own person. Longchamp, bishop of Ely, was left by Richard Coeur de Lion as chief guardian of the kingdom and in charge of the Tower during the King's absence in Palestine. John, by his influence with the citizens, prevailed on them to desert the cause of his royal brother and Longchamp, and the latter, after handing to John the keys of the Tower, escaped, disguised as a woman, to France. During the insurrection of Wat Tyler, the mob, through some unaccountable negligence or treachery on the part of the guard, got within the Tower and overran its apartments, insulting the Princess of Wales, the mother of Richard II., and dragging forth from their refuge in the chapel Simon, archbishop of Canterbury and chancellor, and Sir Robert Hales, treasurer, both of whom they immediately beheaded. The importance attached to the safe keeping of the Tower appeared in a striking manner at a much later period, when, in 1641, Charles I. roused the whole city and both Houses almost to a frenzy by appointing and persisting in maintaining Colonel Lunsford as Lieutenant of the Tower. The appointment was universally regarded as dangerous and unfit, and the King was at last compelled to recall it. It may be mentioned, as a fact not generally known, that the Lord Mayor receives every three months a list, under the sovereign's sign-manual, of the daily pass-word to the Tower.