In 1121, after heavy fighting with the Seljuks, the troops of the King of Georgia David IV of Georgia besieged Tbilisi, which ended in 1122 and as a result David moved his residence from Kutaisi to Tbilisi, making it the capital of a unified Georgian State and thus inaugurating the Georgian Golden Age. From 12–13th centuries, Tbilisi became a regional power with a thriving economy and astonishing cultural output. By the end of the 12th century, the population of Tbilisi had reached 100,000. The city also became an important literary and cultural center not only for Georgia but for the Eastern Orthodox world of the time. During Queen Tamar's reign, Shota Rustaveli worked in Tbilisi while writing his legendary epic poem, ''The Knight in the Panther's Skin''. This period is often referred to as "Georgia's Golden Age" or the Georgian Renaissance.