The Battle of Ascalon is worth noting mostly insofar as it’s recognized as the “end” of the First Crusade. Of course, most Crusades historians nowadays will probably tell you that numbering the Crusades makes little sense (the flow of European soldiers to the east was not nearly that organized) and actually obscures the fact that the Crusader states along the eastern Mediterranean coast were a continuous presence there for almost two centuries, quite apart from the various calls for Crusade that went on in Europe. But still, the First Crusade is maybe more definable than some of the others in the sense that it had a clear beginning (duh, it was the first one) and a clear end (the successful conquest of Jerusalem). Ascalon is considered the final end of the campaign because it secured the conquest of Jerusalem and, perhaps more to the point, because most of the knights of the Crusade left the Holy Land immediately afterward.
Ashkelon, which was called “Ascalon” by the Crusaders (and me, for the purposes of this post), is located on the southern Mediterranean coast of modern Israel (just north of the border with Gaza). At the time, it was controlled by the Fatimid Caliphate of Egypt, and so you can see why the Crusaders felt that its capture was necessary to protect Jerusalem from a Fatimid effort to recapture that city. This was doubly true given that there was a newly-arrived Fatimid army sitting in Ascalon at that very moment, preparing an imminent march to Jerusalem. Godfrey of Bouillon, the ruler of Jerusalem, marched his army toward Ascalon on August 10 and was joined along the way by the army of Raymond of Toulouse, who was still peeved about getting passed over for Godfrey but was willing to bury the hatchet in the face of a major Muslim threat against the city.
Together the Crusaders had an army that was probably about 10,000 men strong, far fewer than the number assembled by Fatimid vizier al-Afdal Shahanshah at Ascalon. They assembled with Godfrey commanding the left flank, Raymond on the right, and the more junior commanders (Tancred, Robert of Normandy,and Robert of Flanders) in the center. I say that al-Afdal was the Fatimid “vizier,” but you should understand that by this point in Fatimid history the caliphs were a complete afterthought in terms of having any actual authority, and so al-Afdal was the de facto ruler of the Fatimid caliphate. The Fatimids probably had somewhere in the neighborhood of 20,000-30,000 men, though it may have been higher than that. However, they apparently felt so certain that the Crusaders would elect to stay within Jerusalem’s walls that they were totally unprepared when the Crusader army arrived at their camp outside Ascalon’s walls. Godfrey and Raymond literally caught them sleeping, and the battle was a total rout. The Fatimids likely lost more men than the Crusaders had in their entire army.
The remainder of the Fatimid army, with al-Afdal, hightailed it back to Egypt post-haste, but Ascalon’s garrison refused to surrender. It was then that the old Crusader bickering that we’ve come to know and love quashed their chances to actually capture the city. Godfrey claimed the city for Jerusalem, but Raymond claimed it for himself, and while they tried to sort out their grievances the Crusader knights started to wonder what the hell they were still doing in the Holy Land when the thing they’d all signed on to do (their “pilgrimage,” i.e. capturing Jerusalem) was already done. Once the knights started leaving to go back home there was no chance for the Crusaders to take Ascalon, and so it remained in Fatimid hands. It wasn’t until 1153, when the Fatimids were really on life support, that the Crusaders finally were able to capture it.