Alexius’s first goal was to recapture Nicaea (now Iznik), a city that lay on the shores of Lake Askania, southeast of Constantinople. The Seljuk Turks had captured this city and their Sultan, Kilij Arslan brazenly declared Nicaea his capital. They posed the greatest threat to Byzantium because of Nicaea’s close proximity to Constantinople. For that reason, it wouldn’t take much effort for the Turks to march north and invade Constantinople. Determined and ferocious, the Turks resisted every Byzantine attempt to re-conquer Nicaea. But now, Alexius had an immense Latin army at his disposal and he was prepared to unleash them, confident that they would drive the Turks out of Nicaea for good.
Since summer was fast approaching, Alexius was anxious to move the crusaders along, and the crusaders, themselves, were growing impatient.
It was a perfect time for the crusaders to lay siege to Nicaea because Kilij Arslan was embroiled in conflict with the Danishmend princes over the suzerainty of Melitene on his eastern frontier. His easy defeat of Peter the Hermit’s army taught Kilij Arslan that the crusaders were nothing more than a bunch of unskilled, rabble-rousers, so he did not fear them. He couldn’t have been more wrong.
Just as he was the first prince to arrive in Constantinople, Godfrey of Bouillon was the first to march on Nicaea. He left Pelecanum sometime the end of April, his army joined by that of Bohemond’s which as commanded by Tancred, as well as Peter the Hermit and what remained of his following. Bohemond stayed in Constantinople and arranged with the emperor provisions for the crusaders: siege engines, food, armor and Byzantine soldiers.
Godfrey and Tancred’s combined forces arrived at Nicaea in early May, followed by those of Robert of Normany, Raymond, Count of Toulouse, the Bishop Adhemar of Le Puy and Stephen of Blois one month later.
The crusaders saw almost right away that, to conquer Nicaea, would be no easy feat. It was heavily fortified: encircling the city was a 10 meter (33 foot) tall wall that was nearly 5 kilometers (3 miles) long in circumference. The wall boasted 114 towers from which warriors could keep watch for enemy advancement, and the western wall rose almost right out of Askanian Lake. The only way to attack the city at its west end was by boat, but the crusaders had no boats. Neither did the 2,000 Byzantine infantry — commanded by General Tatikios — who accompanied them. So, the one and only option to lay siege was to encircle the south, north and east walls, cutting Nicaea off from the outside world. Godfrey’s army blockaded the northern wall; Tancred positioned his troops outside the eastern wall; Raymond of Toulouse and the remaining princes took the southern wall.
France, John. “The First Crusade: Impelled by the Love of God” in Crusades: The Illustrated History. Ed. Thomas Madden. London; Duncan Baird Publishers, 2004.
Runciman, Steven. A History of the Crusades: The First Crusade. Vol.1. Cambridge; Cambridge University Press, 1951.