After the fall of the Ostrogothic Kingdom, the town came under the protection of the Byzantine Empire. Dubrovnik in those medieval centuries had a Roman population. In 12th and 13th centuries Dubrovnik became a truly oligarchic republic, and benefited greatly by becoming a commercial outpost for the rising and prosperous Serbian state, especially after the signing of a treaty with Stefan the First-Crowned. After the Crusades, Dubrovnik came under the sovereignty of Venice (1205–1358), which would give its institutions to the Dalmatian city. In 1240, Ragusa purchased the island of Lastovo from Stefan Uroš I king of Serbia who had rights over the island as ruler of parts of Hum. After a fire destroyed most of the city in the night of August 16, 1296, a new urban plan was developed. By the Peace Treaty of Zadar in 1358, Dubrovnik achieved relative independence as a vassal-state of the Kingdom of Hungary. Ragusa experienced further expansion when, in 1333, Serbian emperor Stefan Dušan, sold Pelješac and Ston in exchange for cash and an annual tribute at the moment when her connection with the rest of Europe, especially Italy, brought her into the full current of the Western Renaissance.