RYBINSK. (Rybnaya Sloboda) Known since 1137, it has been a trade and shipping center for traffic between Moscow and Arkhangelsk since the 16th cent. The Mariinsk Waterway, built in 1810, linked Rybinsk with the Baltic for the first time. In the 1870s it developed as a shipping point to St Petersburg. The construction of the Volga-Baltic canal system increased its importance as a river port. In the 18th century, the Sloboda continued to thrive on the Volga trade. Catherine the Great granted Rybnaya Sloboda municipal rights and renamed it Rybinsk.   It was a place where the cargo was reloaded from large Volga vessels to smaller boats capable of navigating in the shallow Mariinsk Canal system, which connects the Russian hinterland with the Baltic Sea. With the population of 7,000, the town daily accommodated up to 170,000 sailors and up to 2,000 river vessels. Consequently, the local river port became known as the "capital of barge-haulers".