Starting in 1120, King David began a more aggressive policy of expansion, penetrating as far as the Araxes river basin and the Caspian littoral, and terrorizing Muslim traders throughout the South Caucasus. By June 1121, Tbilisi had actually been under a Georgian siege, with its Muslim élite being forced into paying a heavy tribute to David IV. The resurgence of Georgians’ military energies, as well as his demands for tribute from the independent city of Tbilisi brought about a coordinated Muslim response. In 1121, Sultan Mahmud b. Muhammad (1118–1131) declared a holy war on Georgia.