Lake Seliger
The "Novgorodian First Chronicle" relates that Mstislav the Bold launched his campaign against his son-in-law, Yaroslav Vsevolodovich on March 1, 1216, leading a Novgorodian army into his own districts around Lake Seliger at the head of the Volga, where they were told "Go out foraging but take no heads." Sviatoslav Vsevolodovich, the fourth son of Vsevolod the Big Nest, invested Rzhevka with 10,000 men, but Mstislav and Vladimir of Pskov broke the siege with, according to the chronicle, a mere 500 men and Sviatoslav fled.