1750-1799

These canals and locks are a part of the first extensive system of canal and river navigation works undertaken in the United States. The idea for the canal was proposed by George Washington, when, as an engineer, surveyor and military emissary for Virginia, he saw the need for a trade route west beyond the Allegheny Mountains. In order to do create this route, it was necessary to try to tame the Potomac River which was a wild, unruly stream which only the hardiest of rivermen ever attempted.

The Portland Head Light was the first lighthouse to be constructed in Maine and the first one completed and put into service by the Federal government under the Lighthouse Act of 1789, which moved to place all lighthouses under federal control. While work had begun on the lighthouse in 1787 by the State of Massachusetts which, at that time, had jurisdiction over Maine, it was completed by the Federal government. When this lighthouse was being built, Portland was the sixth largest port in the country, the closest port to Europe and had significant trade with the Caribbean.

In 1794, the Delaware legislature authorized a lottery to fund the erection of ice piers in the harbor at New Castle. The ice harbor was designed to protect anchored ships from storms and ice. At the time, New Castle served as the principal winter port for ships from the Port of Philadelphia because ice on the Delaware River posed such a serious hazard to the wooden-hulled vessels. The harbor was the first of its type on the river and the last one to be maintained as the need for them declined. It served as a model for the other four harbors constructed in the area.

The granite milestones marking the Mason-Dixon Line bear crests from the two parties involved in the land-grant dispute, the families of William Penn and Charles Calvert (also known as Lord Baltimore). 

When Governor James Grant arrived in the newly acquired British colony of East Florida in 1764, he found it devoid of settlers. To increase both the population and commerce with the 13 colonies to the north, he commanded that a road be built from his provincial capital of St. Augustine to Ft. Barrington, Georgia. 

When Joseph Priestley discovered oxygen in 1774, he answered age-old questions of why and how things burn. An Englishman by birth, Priestley was deeply involved in politics and religion, as well as science. When his vocal support for the American and French revolutions made remaining in his homeland dangerous, Priestley left England in 1794 and continued his work in America until his death. His library of some 1,600 volumes and his chemical laboratory, where he first isolated carbon monoxide, were probably the best in the country at that time.

Built between 1794 and 1796 by the 22nd King of the Joseon Dynasty, Jeongio, this fortress is an outstanding example of early modern defensive works. Principally designed by Jeong Yak-Yong, it incorporated the most highly developed features of science and engineering from both the east and west.

The stone was set by the joint U.S.-Spanish survey party on April 10, 1799.  Made of sandstone, it is roughly two feet high and eight inches thick. On the north side of the stone is the inscription "U.S. Lat. 31, 1799." On the south side is "Dominio de S.M. Carlos IV, Lat. 31, 1799."

The Choate Bridge of Essex County, completed in 1764, is the oldest documented two-span masonry arch bridge in the United States. Named after Colonel John Choate, who supervised the construction, the bridge is located on South Main Street and spans the Ipswich River. Originally, the bridge measured 80 feet 6 inches long and 20 feet 6 inches wide. In 1838 it was widened to 35 feet 6 inches on the east side in order to accommodate another lane of traffic. The west side and the parapet of the bridge, along with the inscription to Colonel Choate, remained unchanged.

The Old Cape Henry Light house was the first construction project authorized by the First Congress. Constructed by John McComb, Jr. of New York City, this project set the stage for all subsequent public works projects of the Federal Government. In addition, this specific lighthouse was a vital navigation aid to all shipping through the Virginia Capes, thereby enhancing international and coastal trade with the Mid-Atlantic States.