Bulgarian Empire. Although the Bulgarian commander of the fortress of Veroia, Dobromir, was married to one of Samuel's nieces, he voluntarily surrendered the fort and joined the Byzantines. The Byzantines also captured the fortress of Kolidron without a fight, but its commander Dimitar Tihon managed to retreat with his soldiers and join Samuel. The next town, Servia, did not fall so easily; its governor Nikulitsa organized the defenders well. They fought until the Byzantines penetrated the walls and forced them to surrender. Nikulitsa was taken to Constantinople and given the high court title of patrician, but he soon escaped and rejoined the Bulgarians. He attempted to retake Servia, but the siege was unsuccessful and he was captured again and imprisoned. Meanwhile, Basil II's campaign reconquered many towns in Thessaly. He forced the Bulgarian population of the conquered areas to resettle in the Voleron area between the Mesta and Maritsa rivers. Edessa resisted for weeks but was conquered following a long siege. The population was moved to Voleron and its governor Dragshan was taken to Thessaloniki, where he was betrothed to the daughter of a local noble. Unwilling to be married to an enemy, Dragshan three times tried to flee to Bulgaria and was eventually executed. War with Hungary The Byzantine–Bulgarian conflict reached its apex in 1003, when Hungary became involved. Since the beginning of the 9th century, the Bulgarian territory had stretched beyond the Carpathian Mountains as far as the Tisza River and the middle Danube. During the reign of Samuel, the governor of these northwestern parts was duke Ahtum, the grandson of duke Glad, who had been defeated by the Hungarians in the 930s. Ahtum commanded a strong army and firmly defended the northwestern borders of the Empire. He also built many churches and monasteries through which he spread Christianity in Transylvania.Venedikov, p. 150. Although Gavril Radomir's marriage to the daughter of the Hungarian ruler had established friendly relations between the two strongest states of the Danube area, the relationship deteriorated after Géza's death. The Bulgarians supported Gyula and Koppány as rulers instead of Géza's son Stephen I. As a result of this conflict, the marriage between Gavril Radomir and the Hungarian princess was dissolved. The Hungarians then attacked Ahtum, who had directly backed the pretenders for the Hungarian crown. Stephen I convinced Hanadin, Ahtum's right-hand man, to help in the attack. When the conspiracy was uncovered Hanadin fled