Original Conestoga wagons had large, broad wheels and usually were pulled by six horses. The name for the wagon was taken from the region in Pennsylvania where they first were built in the 18th century. Conestogas primarily were used to carry heavy loads of freight across the prairies of the United States. The large wheels enabled them to pass over ruts and through the mud of the prairie roads. The large canvas cover was used for protection against bad weather. An unusual feature of the Conestoga wagon was its floor, which was shaped to prevent freight loads from shifting. The prairie schooner was a later development of the Conestoga wagon, a name that came from its white top that gave it the appearance of a sailing ship. It had a flat floor, lower sides, and was simpler and less expensive to construct.