The first major siege of the first crusade. The danger Byzantium stood in is amply demonstrated by the presence of the Seljuk Turks at Nicaea, a major fortified city only fifty miles from Constantinople. The city was strongly defended by four miles of walls, and it's position on a lakeside made it very difficult to blockade. The crusaders relied on Byzantine aid, at least after their initial attempts to take the city by storm had failed. The Crusaders eventually settled down for a proper siege, but even then their efforts to undermine the walls resulted in failure when a tunnel being dug under the walls collapsed early, allowing the defenders to repair the damage. It was only when the Byzantines transported a fleet onto the lake facing Nicaea that the defenders decided to negotiate a surrender. The crusaders woke to find the city unexpectedly in Byzantine hands, and were angered by Alexius's refusal to let them to sack the city as was normal, a dispute in which both sides had some justification, the crusaders have endured the rigors of carrying out a siege, while to Alexius the city was part of his empire, only temporarily lost to the Turks, and so not to be damaged. This dispute only served to worsen the already bad relations between the Byzantines and the crusaders.
Nicolle, David, The First Crusade 1096-1099: Conquest of the Holy Land , Osprey Campaign Series, vol 132. The Osprey volume for the first crusade. Nicolle had a great depth of knowledge of middle-eastern history, which is reflected in this book.
