On August 28, 1189, a Crusader army under the command of “King of Jerusalem” (in reality Saladin had captured Jerusalem almost 2 years earlier) Guy of Lusignon laid siege to the city of Acre, which Saladin had also conquered on his way to Jerusalem. The siege would last almost two years until the Crusaders, by then led by King Richard I of England, King Philip II of France, and Duke Leopold V of Austria, conquered the city in July 1191. The Internet History Sourcebook, at Fordham University, has a primary source account of the siege, a translation of the Latin chronicle Itinerarium Peregrinorum et Gesta Regis Ricardi:
Acre was hemmed in on all sides, besieged by an infinite multitude of people, people from every Christian nation under heaven, people chosen from all the Christians, people well fitted for war and unremitting labor. The people had now besieged Acre for a very long time and they had been troubled by many afflictions, by constant labors, by shortages of food, and by many adversities, as has in part been pointed out above.
There appeared beyond them, furthermore, an innumerable army of Turks, who covered the mountains and valleys, bills, and plains. Here and there they fixed their tents, made of various patterns of flowing colors.
They also saw the pavilions of Saladin and the tents of his brother, Saif adDin, and of Taki adDin, the steward of paganism. The latter superintended the sea and the fort, and he frequently set up assaults and serious attacks against the Christians.
King Richard seemed to be sizing up all their armies. When he put into port, the King of France and the magnates, commanders, and great men of the armies there marched out to him. They received him with joy and exultation, for they had very much desired his arrival…
Acre was the high water mark of the Crusade, since (and nobody could have predicted this) the Christian kings fell to squabbling with each other shortly after. For one thing, Holy Roman Emperor Frederick Barbarossa drowned crossing a river on the way to the Holy Land, so most of the German troops were either killed in the resulting chaos or simply returned home without ever getting to Acre. Leopold and his men cut out after Acre because he was tired of the two kings, Richard and Philip, treating him as an inferior just because he was a mere duke. Then Philip and the French soldiers left because he and Richard were backing two different claimants to the throne of “Jerusalem” (Richard supported Guy while Philip backed Conrad of Montferrat, who probably had the better legal claim).
This left Richard, who showed himself to be Saladin’s equal as a commander by winning the Battle of Arsuf in September 1191, without the raw numbers needed to threaten Jerusalem. He looked to ally with the only other sizable Christian army in the region, Conrad’s, but Conrad understandably told him to go spit. Richard eventually had to accept Conrad as King of “Jerusalem,” but Conrad was assassinated shortly thereafter, probably at Richard’s behest. Then the army couldn’t agree on whether to squeeze Saladin by attacking his base in Egypt (Richard’s preferred plan), or to besiege Jerusalem directly. Richard laid one last defeat on Saladin, at Jaffa in August 1192, at which point Saladin agreed to allow Christian pilgrims into Jerusalem in exchange for the destruction of Richard’s fortifications at Ascalon (Ashkelon today), and Richard departed for home.
Despite its failure to retake Jerusalem, the Third Crusade is considered a success in that it rolled back much of Saladin’s conquests and established a stable Latin kingdom in the Holy Land, centered at Acre. For his trouble, Richard was imprisoned by Leopold when he tried to cross Austria on his way back to England, on suspicion that he’d had Conrad (who was Leopold’s cousin) murdered, and had to deal with his brother John’s usurpation of the throne when he finally did get home.