The Sioux lived in tepees, portable tents made of animal skins or birch bark and long, wooden support poles. The tepee was a durable shelter that kept inhabitants warm in the winter, cool in the summer, and dry during thunderstorms. The tepee was easily constructed and deconstructed, which made it advantageous when following buffalo herds hundreds of miles through the Great Plains. The tepee was also designed to enable its inhabitants to light indoor fires. Sioux tepees were built with two smoke flaps at the top, which could be adjusted with poles to prevent the wind from blowing inside the structure. Prior to the arrival of the Europeans, the travois was used to transport the tepees and family belongings. A travois was a “V-shaped” formation of tree trunks dragged by a team of dogs. After the Europeans arrived, the Sioux became dependent on horses and were known as accomplished riders.