Complex sentence: He was a major builder of caravanserais, bridges, baths, and mosques in towns such as Kaçanik in Kosovo, and important buildings in Thessalonika, Belgrade, and Istanbul and in other countries in the Arab world.
Split into simpler sentences: He was a major builder of caravanserais, bridges, baths and mosques. These included the town of Kaçanik in Kosovo, important buildings in Thessalonika and Belgrade, as well as in Istanbul and other countries in the Arab world.