With a force of 7,000-9,000 infantry and 400-700 knights (including 200 knights from King William II of Sicily) and 52 ships from Ulbado Lanfranchi, Arshbishop of Pisa, King Guy attempted to storm the city walls on 28 August 1189. The attack failed so Guy laid siege and waited for reinforcements, which started to arrive a few days later.
Danish and Frisian fleets replaced the Sicilian fleet, which withdrew on the death of William II. Guy's army swelled, and numbered 30,000 infantry and 2,000 cavalry by the end of September, with at least 102 ships. Muslim writers noted a number of warrior women among the European forces.
Following Salah ad-Din
's inconclusive victory at the Battle of Acre
on 4 October 1189 more European ships arrived, and Guy was able to blockade the city. An Egyptian fleet relieved the blockade on 17 December, but Conrad of Tyre sent supplies, which Guy used to build siege engines, lost in a failed attack on the city on 6 May 1190.
On 20 May 1190 Salah ad-Din led and assult on the Christian camp but was repelled after 8 days' fighting. Salah ad-Din then laid a countersiege to contain the Christians.
Epidemics soon spread in the Christian siege camp. The daughters of Guy and Queen Sibylla of Jerusalem died between late July and October, and a few days afterwards Sibylla also died. Since she was heir to Jerusalem, Guy lost his claim to the throne but refused to step aside in favour of Sibylla's heir, her half-sister Isabella of Jerusalem.
In winter of 1190-1191 Crusader leaders including Theobald of Blois and Stephen of Sancerre died, as did Patriarch Eraclius. Henry of Champagne fell ill, but recovered after many weeks. Duke Leopold V of Austria arrived and took command of Christian forces. The reinforcements brought news that the Kings of France and England were on their way.
On 6 January 1191 part of the city walls collapsed following several attempts to breach them. Christian forces made many attempts to take advantage of the collapse, but could not.
King Philip of France arrived on 20 April, and King Richard of England on 8 June. King Philip had built siege engines, and assaulted the city on 17 June, against the wishes of King Richard, who had been ill. The attack was repulsed.
On 2 July King Richard led his own attack, with the enormous mangonels God's Own Catapult and Bad Neighbour, creating a sufficient breach on 3 July. On 4 July the city offered its surrender, but Richard refused the terms and continued his assault. On 7 July the city asked Salah ad-Din for help, but he was unable to do so and after a final battle on 11 July the city offered terms acceptable to King Richard on 12 July. Salah ad-Din accepted the surrender following negotiations between his representative and Conrad de Montferrat. The Christians entered the city and captured the garrison. Conrad flew the banners of Duke Leopold, King Philip and King Richard over the city. Richard had Duke Leopold's banner torn down, which caused Leopold to withdraw from the city and return to Austria.
On 31 July 1191 King Philip left Acre to settle a succession dispute in Vermandois and Flanders, leaving King Richard on sole command of the Christian forces.