1.The Port on the Coastal Road
Sozopol lies at the southern end of the Gulf of Burgas, on the great Black Sea road that ran from Constantinople through Derkos, Agathopolis, Sozopol, Anchialos and Varna to the Danube delta. By land the Byzantine army covered this road slowly, while by sea ships could reach the Danube mouths from the capital in about ten days. That is why the coastal fortresses — Anchialos, Develt, Sozopol and Ranuli on the Ropotamo — were already key positions in the time of Khan Krum, when the left wing of his army was stationed precisely in them.
2.Between Two States (Thirteenth to Early Fourteenth Century)
In the thirteenth century Sozopol was a Byzantine town. From here came the monk Kosmas, later called "the Sozopolitan", who on 1 January 1294 was raised to the patriarchal throne of Constantinople as John XII. The former patriarch later played a part in Bulgarian-Byzantine relations as well: he was sent to Constantinople with Theodore Svetoslav's proposal of peace and a marriage alliance, which Andronikos II put off but was finally forced to accept.
The road to peace ran through war. When Theodore Svetoslav's army appeared near Sozopol in 1304, a Byzantine force was sent against it under Voysil, brother of the former tsar Smilets, and the sebastokrator Radoslav. After several smaller clashes — in one of which, near Sozopol, the Byzantines won — the Bulgarians won the decisive battle on the river Skafida, broke through the Byzantine lines and laid waste the district of Adrianople.
3.The Genoese Ban and the Change of Rule (1316–1332)
Sozopol was also an important point in Black Sea trade. On 22 March 1316, at the height of a conflict with Bulgaria, Genoa's Office of Gazaria forbade its citizens to go to any part of Zagora — Bulgaria — and expressly to visit the port of Sozopol; notaries were forbidden to draw up documents for voyages there.
When Tsar George II Terter died in the spring of 1323, the whole strip from Sliven to the sea passed to Byzantium without a fight — Sozopol, together with Yambol, Rusokastro, Anchialos, Agathopolis and several other fortresses, accepted the emperors of its own accord. Peace between Michael III Shishman and Andronikos III was concluded in late 1328 or early 1329 at Krimni, between Sozopol and Anchialos, and after the victory at Rusokastro in 1332 the coast was again under Ivan Alexander's rule.
4.The Last Decades (1332–1366)
In the mid-fourteenth century Sozopol was part of the Bulgarian tsardom. The Venetians had a colony here alongside those at Varna, Mesembria and Anchialos, buying chiefly grain, hides, wax and honey.
The end of Bulgarian rule came with the campaign of Amadeus VI of Savoy. On 4 October 1366 his 14 ships set out for the Bulgarian coast and soon took Agathopolis, Sozopol and Skafida. In the agreement that followed John V's release, Sozopol, together with Mesembria and Anchialos, was ceded to Byzantium. In one of his letters to the emperor the pope reported that he had consecrated the Dominican William Conti as Latin bishop of Sozopol.