Ice floes could crush wooden-hulled ships, so piers were built to form a barrier sheltering New Castle harbor. These were the first constructed anywhere on the Delaware River. An initial set of three was funded by state lottery and installed in 1795 and 1801. An act of Congress in 1802 appropriated $30,000 for many more Delaware River piers, provided the sites were ceded to the federal government. The Latrobe-Mills survey of 1805 shows four “U.S. Piers,” results of the first nonmilitary federal funding applied to the Delaware. Further piers were added later, until the ascendancy of iron-hulled ships rendered them unnecessary. Today there are seven in all. The two oldest, square in plan, lie at the foot of Harmony Street and along the silted-up shoreline at Alexander's Alley. The five hexagonal-plan piers, left to right as seen from shore, respectively date to 1874, 1879, 1882, 1875, and 1854 (the last now linked to shore by a walkway). The piers are rubble-cored with ashlar granite blocks outside, resting on wooden cribwork (visible at low tide). Some granite mooring posts and iron straps survive. The Ice Piers were a precursor to a much larger project at Lewes (ES25).