The pretzel can be traced back to the Romans, although the twisted loose knot shape is thought to have been introduced in the early part of the 7th century. The first U.S. commercial pretzel factory was established in 1861 in Lititz, Pennsylvania. There are two main types of pretzel-hard and crisp or soft and chewy (the older of the two forms). The latter is often sold hot with mustard by street vendors from their pretzel carts. Pretzels can be sprinkled with coarse salt or not, and shaped in the form of knots, sticks or rings. Crisp pretzels are available in many sizes, shapes and even flavors (such as rye) in supermarkets.