An historian of early Russian history faces many methodological problems, not the least of which is the paucity of sources for the Kievan and Mongol periods. Because of the dearth of material, historians of the medieval Russian town, such as M. N. Tikhomirov and A. M. Sakharov, have generally presented a static conceptualization of urban society, thereby obscuring the dynamic processes and nuances of historical development. Despite the many studies of Novgorod, one can fairly state that historians have often described fourteenth and fifteenth-century Novgorod as though it were virtually unchanged since 1136, when the town declared its independence from Kiev. While recognizing the importance of the Sovet gospod (Council of Lords) and posadnik (mayor), some historians have nevertheless insisted that the veche (assembly) was the sovereign body of the republic. Its meetings were open to the town's citizens, and though the veche at times degenerated into brawls, no prince or posadnik could effectively govern without its concurrence. Indeed, George Vernadsky characterized Novgorod as a democratic republic, somewhat reminiscent of the Greek polis, while Tikhomirov viewed Novgorod's political traditions as similar to those of the urban communes of medieval Europe.