In 1764, Charlotte Amalie was declared a free port by King Frederick V, and the Town became the busiest harbor in the Caribbean. The American Revolution in the 1770s was good news for the City, as it was thriving times for the local businessfolk.  The Town began to be filled by immigrants from Europe, Africa and the Caribbean, most of them from other islands of the Lesser Antilles. By 1778, the Danish Government had strengthened their military position by building Bluebeard's Castle and Blackbeard's Castle, lookout towers on the crests of the two hills by the City. The City prospered as a free port and United States, Danish, Sephardic, German, French, British, Italian and Spanish importing houses operated here. At the end of the 18th century, United States founding father and future architect of the United States Constitution, Alexander Hamilton, decided the Town was so wealthy that "gold moved through the streets in wheel-barrows". At one point, the City of Charlotte Amalie in the Danish West Indies was the second-largest city in the Danish Realm, only smaller than the capital of Copenhagen.