 Complete the following phrase:  At the end of the 10th century, Dobruja was the theatre of operations between the Kievan Rus army led by Prince Sviatoslav I, the Bulgarian army and the Byzantine army led by emperor John Tzimiskes. Sviatoslav controlled large parts of the First Bulgarian Empire and established his capital at Pereyaslavets near modern Nufăru on the Danube. The Byzantines, led by John Tzimiskes were on the offensive after they defeated the united Russo-Bulgarian forces in the Battle of Arcadiopolis. Pereyaslavets was captured and Sviatoslav was forced to flee westwards to the fortress of Dorostolon Durostorum. Emperor John proceeded to lay 