to facilitate landings and troop deployments in shallow water. Longships were used extensively by the Leidang, the Scandinavian defence fleets. The longship allowed the Norse to go Viking, which might explain why this type of ship has become almost synonymous with the concept of Vikings. The Vikings built many unique types of watercraft, often used for more peaceful tasks. The knarr was a dedicated merchant vessel designed to carry cargo in bulk. It had a broader hull, deeper draught, and a small number of oars (used primarily to manoeuvre in harbours and similar situations). One Viking innovation was the 'beitass', a spar mounted to the sail that allowed their ships to sail effectively against the wind. It was common for seafaring Viking ships to tow or carry a smaller boat to transfer crews and cargo from the ship to shore. Ships were an integral part of the Viking culture. They facilitated everyday transportation across seas and waterways, exploration of new lands, raids, conquests, and trade with neighbouring cultures. They also held a major religious importance. People with high status were sometimes buried in a ship along with animal sacrifices, weapons, provisions and other items, as evidenced by the buried vessels at Gokstad and Oseberg in Norway and the excavated ship burial at Ladby in Denmark. Ship burials were also practised by Vikings overseas, as evidenced by the excavations of the Salme ships on the Estonian island of Saaremaa. Well-preserved remains of five Viking ships were excavated from Roskilde Fjord in the late 1960s, representing both the longship and the knarr. The ships were scuttled there in the 11th century to block a navigation channel and thus protect Roskilde, then the Danish capital, from seaborne assault. The remains of these ships are on display at the Viking Ship Museum in Roskilde. In 2019, archaeologists uncovered two Viking boat graves in Gamla Uppsala. They also discovered that one of the boats still holds the remains of a man, a dog, and a horse, along with other items. This has shed light on death rituals of Viking communities in the region. Social structure Viking society was divided into the three socio-economic classes: thralls, karls and jarls. This is described vividly in the Eddic poem of Rígsþula, which also explains that it was the god Ríg—father of mankind also known as Heimdallr—who created the three classes. Archaeology has confirmed this social structure. Thralls were