Immediately after the battle, the armies of Murad I embarked on another campaign overrunning Northern Thrace and forcing young Ivan Shishman to pull back north of the Balkan Mountains. A number of fortresses fell, though after prolonged and fierce sieges: the town of Diampol, for instance, fought against the forces of Timurtash for months but was eventually forced to surrender because of food shortage. One of Ivan Shishman's "voivodes", Shishkin, was killed in battle on the southern skirts of the Balkan Mountains further easing the Ottoman conquest of the Rhodopes, Kostenets, Ihtiman, and Samokov. After a bloody siege they captured Bitola in the southwest and soon encroached on the Sofia Valley. In 1373 Ivan Shishman was forced to negotiate a humiliating peace treaty: he became an Ottoman vassal strengthening the union with a marriage between Murad and Shishman's sister Kera Tamara. To compensate, the Ottomans returned some of the conquered lands, including Ihtiman and Samokov.