Battle of Rusokastro The Battle of Rusokastro ( , ) occurred on July 18 , 1332 near the village of Rusokastro , Bulgaria , between the armies of the Bulgarian and Byzantine Empire s . The result was a Bulgarian victory . Origins of the conflict . In 1328 , the emperors of Bulgaria and Byzantium , Michael Asen III and Andronikos III Palaiologos , signed a secret treaty against Serbia . While Michael Asen III was fighting against the Serbs in 1330 , the Byzantines invaded Thrace and captured the Bulgarian towns there . Following the defeat of Bulgaria in the Battle of Velbazhd the Byzantines got a firm foothold there . Prelude . The Byzantines were not ready for war . Their Empire was rent with civil unrest and the army was fighting against the Turks in Asia Minor . In the Bulgarian Empire , there were internecine struggles as well but the new Emperor Ivan Alexander knew that the decisive confrontation with Byzantium was yet to come and decided to improve his relations with the Serbs . In 1332 , he concluded a peace treaty with them which lasted till his death . The treaty was secured with a marriage between the Serb king Stefan Dushan and the sister of the Emperor , Elena . In the summer of the same year , the Byzantines gathered an army and without a declaration of war headed towards Bulgaria , looting and plundering the villages on their way . The Byzantines seized several castles because Ivan Alexander ' s attention was focused towards fighting the rebellion of his uncle Belaur in Vidin . He tried to negotiate with the enemy but ultimately failed . The Emperor decided to act swiftly during the course of five days whereby his cavalry covered 230 km to reach Aitos and face the invaders . The battle . Ivan Alexander had troops of 8 , 000 while the Byzantines were only 3 , 000 . There were negotiations between the two rulers but the Bulgarian emperor deliberately prolonged them because he was awaiting reinforcements . In the night of July 17 they finally arrived in his camp ( 3 , 000 cavalry men ) and he decided to attack the Byzantines the next day . Andronikos III Palaiologos had no choice but to accept the fight . The Byzantine army consisted of 16 squads and six of them made up the first column . The right wing was commanded by the " protostrator " , the left wing was under the " megas papias " Alexios Tzamplakon , and the center was commanded personally by the emperor . The army formed a wide front in two lines with the flanks positioned behind the center forming a crescent . The battle began at six in the morning and continued for three hours . The Byzantines tried to prevent the Bulgarian cavalry from surrounding them , but their manoeuvre failed . The cavalry moved round the first Byzantine line leaving it for the infantry and charged the rear of their flanks . After a fierce fight the Byzantines were defeated , ran away from the battlefield and hid in Rusokastro . The Bulgarian army surrounded the fortress and at noon on the same day Ivan Alexander sent envoys to continue the negotiations . Aftermath . The Bulgarians returned their lost lands in Thrace and strengthened the positions of their empire . The eight - year old son and successor of the Bulgarian emperor Michael Asen was married to the daughter of Andronikos , Maria , confirming the peace between the two countries . This battle was considered by the medieval Bulgarian historians as a great triumph of emperor Ivan Alexander . That was the last major battle between Bulgaria and Byzantium as their seven - century rivalry for domination on the Balkan was soon to come to an end after the fall of the two Empires under Ottoman domination . Rusokastro Rock at the north entrance to McFarlane Strait in the South Shetland Islands , Antarctica is named after “ the settlement and medieval fortress of Rusokastro in Southeastern Bulgaria . ”