The penultimate Russo-Byzantine War, as documented by medieval Greek sources, took place in 1024, when a relative of the Kievan

Kievan Rus'

Kievan Rus was a medieval polity in Eastern Europe, from the late 9th to the mid 13th century, when it disintegrated under the pressure of the Mongol invasion of 1237–1240....

 prince with 800 men and 20 ships penetrated into the Bosporus

Bosporus

The Bosphorus or Bosporus , also known as the Istanbul Strait , is a strait that forms part of the boundary between Europe and Asia. It is one of the Turkish Straits, along with the Dardanelles...

 and, defeating a unit of the Greek coast guard, sailed into the Aegean Sea

Aegean Sea

The Aegean Sea[p] is an elongated embayment of the Mediterranean Sea located between the southern Balkan and Anatolian peninsulas, i.e., between the mainlands of Greece and Turkey. In the north, it is connected to the Marmara Sea and Black Sea by the Dardanelles and Bosporus...

. The Kievans reached the island of Lemnos

Lemnos

Lemnos is an island of Greece in the northern part of the Aegean Sea. Administratively the island forms a separate municipality within the Lemnos peripheral unit, which is part of the North Aegean Periphery. The principal town of the island and seat of the municipality is Myrina...

, where they were annihilated by a much stronger Byzantine fleet. The conflict is not documented in Kievan sources and its motivation is obscure.