Pennsylvania, one of the original thirteen colonies, became the second state of the US. Pennsylvania territory had been disputed in the early 1600s among the Dutch, the Swedes, and the English. Philadelphia was the seat of the early US federal government almost continuously from the year 1776 to 1800. Sometimes called the "Keystone State", Philadelphia is rich in historic ties to the founding of America. The U.S. Constitution was signed in Philadelphia and on December 12, 1787. The Declaration of Independence was signed in 1776 in this state. Pennsylvania is the 33rd largest state in the US., with an area of 46,058 square miles. In population, Pennsylvania is the sixth most populous state in the USA with 12,406,292 (from a 2004 estimate) Steel production is one of the states main industries. Although farming, and dairies account for much of the industry. Leading commodities are dairy products, cattle, mushrooms, greenhouse and nursery products, poultry, a variety of fruits, sweet corn, potatoes, maple syrup, and Christmas trees. Some of the states main rivers are the Allegheny River,the Susquehanna River, the Delaware River, and the Ohio River. Bordering States include New York to the north, New Jersey, Delaware, and Maryland to the east, West Virginia to the south, and Ohio to the west.