After the returning reconnaissance units reported that the roads were clear, the advance continued. When Mehmed arrived before the fortress of Corinth, he established his camp there. The following day, he took some of his commanders with him to inspect the hill dominating the city and to determine from where an assault might be launched. In this way, they realized that the fortress would not easily yield, as the city was situated on high ground and surrounded by steep and sheer rocky terrain. Although Mehmed demanded the city's surrender, the garrison refused. In order to place the defenders in difficulty by cutting off supplies, Mehmed devastated the surrounding fields and wheat crops. He then encircled the city with his troops and positioned siege equipment around the walls.[7]
After leaving a portion of his army to continue the siege of the fortress, Mehmed II personally led raiding parties into the interior of the Morea in small detachments. The forces under Ömer Bey compelled the fortresses of Tarsos, Akova, Rupela, Pazenika, Kalavryta, and Leondari to surrender. Mehmed II himself entered the territory belonging to Dimitrios Asanes and captured the fortresses of Muhlion, Patras, and Vostitsa.[8]
Mehmed II then returned to Corinth. The fortress and the city had still not been taken. Due to the siege, which had lasted for four months, the soldiers had grown weary and wished to abandon it. However, Mehmed II declared that the fortress would be taken no matter what. After addressing the demands and restoring the morale and determination of his commanders and soldiers, the Ottoman army regained its spirit and prepared once again for the siege.[9]
The Ottoman artillery, however, could only be moved as far as the foot of the fortress. In response, Mehmed II had bronze transported to the Church of Hagios Nikolaos in front of the fortress and ordered the casting of four powerful siege cannons there. The Ottomans successfully applied mobile artillery casting techniques and tactics at this location. Mehmed II then resorted to another stratagem, telling the envoys of the Morea to inform their lord that he wished to speak with him personally and was considering peace. Through this ruse, he lured Despot Demetrios's cavalry force of 6,000 men into the open and defeated them in a sudden maneuver, thereby routing the army that was coming to relieve Corinth.[10]
The commander of the fortress was Mateos Asanes. With Venetian assistance, Asanes had managed to obtain additional troops and supplies. The sultan ordered the massive cannon to be positioned opposite the fortress. The cannonballs, weighing hundreds of kilograms, were fashioned from the ruins of ancient Corinth. In accordance with Islamic tradition, Mehmed once again called upon the defenders to surrender. Confident in the strength of the walls and the garrison, Asanes rejected the offer. Mehmed then brought his great cannons into action. The outer wall was demolished within a few days. After launching a counterattack, Asanes withdrew to the second wall, but this too collapsed under heavy artillery fire.[11]
At the third wall, Mehmed's troops launched an assault. A fierce battle ensued, with both sides killing and wounding one another as their cries rose to the sky. They fought at such close quarters that the combat became hand-to-hand. Nevertheless, the attacks failed to achieve success, as the garrison's frontal resistance, long spears and pikes, and large stones hurled from the walls struck down many of the besiegers at the front. Thereupon, the sultan ordered his troops to withdraw beyond the range of arrows and swords.[12]
By this point, however, famine had begun to take hold within the fortress. Mehmed continued the bombardment. Eventually, Mateos Asanes and Nikephoros Loukanes went to the sultan's camp and surrendered the fortress under terms of peace. Mehmed left Ömer Bey behind as sancak governor and began his return march toward Edirne. During this campaign, Mehmed had brought 250 Greek settlements under his control.[13]