The city of Silves in the Almohad Caliphate was besieged from 21 July until 3 September by the forces of Portugal and a group of crusaders from northern Europe on their way to the siege of Acre.

One of these sacked Alvor and massacred its inhabitants some weeks before the fleet that would attack Silves had assembled in Lisbon in early July.

[2] The next most important source, the Ymagines Historiarum of the English chronicler Ralph of Diceto, is also in Latin and from a northern perspective.

There is confusion in some sources, such as the Itinerarium peregrinorum et gesta regis Ricardi and the Chronicon of Robert of Auxerre, between the sack of Alvor and the capture of Silves.

[1] Nevertheless, Robert's account made its way into the chronicle of William of Nangis, the Chronicon Turonense and a lost work by a certain Hugo, copied by Vicente Salgado [pt] into his Memorias Ecclesiasticas do Reino do Algarve.

[15] The author of the Narratio calls the walled section leading to the river a corrasce, from the local Romance word couraça, "breastwork".

[19] In October 1187, Jerusalem was captured by the Ayyubids and Pope Gregory VIII issued a call for a new crusade to recover it in his bull Audita tremendi.

He records that composition of the crusader company was variable, as some joined up at a later point in the voyage while others left to find their own way to the Holy Land.

[27] After purchasing one replacement ship in London, the fleet left Sandwich on 19 May and sailed west along the coast of England to Winchelsea, Yarmouth (23 May) and Dartmouth (24 May).

[28][29] Some men of London which the Gesta regis Henrici secundi records as present at the fall of Silves may have joined the fleet at this time.

On 20 July, they approached the city on skiffs and, according to the Narratio, "pitched camp so that it was well within double bowshot of the wall.

[52] The camp was moved closer to the walls of the suburb and the crusaders spent the day preparing ladders for an assault the following morning.

After putting up weak resistance with stones and darts, the defenders retreated to the city, leaving the lower town in the hands of the attackers.

[52] On 22 July, leaving the captured town to be held by the galley crews, the army launched an assault with ladders against the city but was repulsed.

[57] The royal army was said to include "a large number of cavalry, infantry and galley crewmen, and also … religious knights of three types", namely, the Templars, the Hospitallers and the Order of Avis.

[65] On 11 August, the crusaders began mining the walls of the city, but the following day the defenders sortied and burned the tunneling works.

[65] the Narratio notes that at this juncture the defenders were suffering from thirst and there was an increase in desertions: … many people now fled to us at various times from the fortress, in order to save their lives; and to encourage others to leave too we did not harm them in any way.

A new tunnel was begun at a distance from the wall to avoid early detection, but the defenders noticed it and sortied twice, being beaten back a second time on 22 August.

According to the Narratio, the attackers were driven back "with a copious fiery flood" (igneo copioso fluvio), possibly indicating Greek fire.

They accepted 20,000 gold coins, but when it became apparent that it would take some time for the king to gather such a large sum, they withdrew their consent.

[70] This date is found in the Narratio, the Chronicon Conimbricense (which erroneously places it in the year 1190) and Ibn ʿIdhārī (Rajab 20 in the Islamic calendar), indicating that Ralph of Diceto is in error in giving 6 September.

According to the author of the Narratio, some crusaders acted "in defiance of the treaty" by robbing the departing Muslims or even torturing some in the city into revealing their hidden wealth.

[70] According to the Narratio, nine castles that had been governed from Silves came into Portuguese hands after the fall of the city: Lagos, Alvor, Portimão, Monchique, Santo Estêvão, Carvoeiro, São Bartolomeu de Messines, Paderne and Carphanabel.

According to the Narratio, the division of the booty descended into commotion and, to avoid an escalation, the leaders of the crusade turned the city over to Sancho, requesting that he assign them a fair portion of what wealth remained in it, which he did not do.

[76] According to the Narratio, Sancho had also promised to bestow a tenth of the conquered lands to the Church of the Holy Sepulchre in compensation for delaying the crusaders but afterwards reneged.

[73] It is generally thought that this is the same unnamed person who was in command from the beginning of the siege, but Friedrich Kurth argued that the new governor was Álvaro Martins, who is known to have subsequently died at Silves in battle with the Muslims sometime before 27 July 1190.

[73] The author of the Narratio believed that the entire Gharb—including the towns of Faro, Loulé, Cacela, Tavira, Mértola and Serpa—could have been taken if not for Sancho's ill feeling towards the crusaders and the "accursed haste of some of our men.

[73] They passed the island of Saltes, whose inhabitants fled to Huelva at their approach, and were forced by contrary winds to enter the port of Cádiz on 26 September.

When only four prisoners were handed over the next day, the crusaders rampaged, burning down houses, tearing down walls and uprooting vineyards and orchards.

[89] According to the Narratio de primordiis ordinis theutonici, they used wood and cloth from their sailing ships to make a field hospital, a foundation which ultimately evolved into the Teutonic Order.