The origins of the Russian Navy can be traced back to the period between the 4th and the 6th century. The first Slavic flotillas consisted of small sailing ships and rowboats, which had been seaworthy and able to navigate in riverbeds. During the 9th through 12th centuries, there were flotillas in the Kievan Rus' consisting of hundreds of vessels with one, two, or three masts. Riverine vessels in 9th century Kievan Rus guarded trade routes to Constantinople. The citizens of Novgorod are known to have conducted military campaigns in the Baltic Sea (e.g., the siege of Sigtuna in 1187)—although contemporary Scandinavian sources state that the fleet was from Karelia or Estonia. "Lad'ya" ("ладья" in Russian or sea boat) was a typical boat used by the army of Novgorod (length 30 meters with a width of five to six meters, and two or three masts, with the armament of battering rams and catapults, complement: 50 to 60 men). There were also smaller sailboats and rowboats, such as "ushkuys" ("ушкуи") for sailing in rivers, lakes and skerries, "kochis" ("кочи"), and "nosads" ("носады"), used for cargo transportation.