The Viking age lasted from AD 790 to 1100. The Vikings were mainly from Norway, Denmark, and Sweden, and were the best shipbuilders and seamen of their time. They were able to travel long distances in their longships and attack towns on the coasts of Britain and Ireland. They reached Greenland, Iceland, and even America. The Vikings' boats were long, narrow, light, and flexible. They made them out of oak wood. The typical length of a longship was about 20 meters. The hulls of the ships were shallow so that they could dock on beaches and sail in shallow water. A longship had a large, square, woolen sail, which the Vikings covered in horse fat to make it waterproof. The main power for the longship was from the oars, which were all along the ship. There were usually a crew of about 60 men who rowed the boat. The sailors usually placed their shields along the side of the boat for protection. They also carved the fronts of their ships into the shape of a dragon's head in order to scare the enemies.