 Complete the following phrase:  In 860, the Rus under Askold and Dir launched their first attack on Constantinople from Kiev. The result of this attack is disputed, but the Varangians continued their efforts as they regularly sailed on their monoxyla down the Dnieper into the Black Sea. The Rus raids into the Caspian Sea were recorded by Muslim authors in the 870s and in 910, 912, 913, 943, and later. Although the Rus had predomitly peaceful trading relations with the Byzantines, the rulers of Kiev launched the relatively successful naval expedition of 907 and the 