Chatham’s twin lights evolved through three generations of lighthouse towers on the bluff at James Head overlooking Chatham Harbor and the Atlantic at the elbow of Cape Cod. The earliest complex, built in 1808, consisted of two 40-foot octagonal wooden towers with fixed beams from oil lamps and reflectors, tended by keeper Samuel Nye, appointed by President Thomas Jefferson. In 1841, those aging structures were replaced by white brick towers, and in 1857 each received a fourth-order Fresnel lens fueled by lard oil lamps. After a fierce 1870 Nor’easter exposed the bluff to severe erosion, the lights were moved inland in 1877 to a third set of cast-iron towers lined with brick. The lantern room preserved here dates from 1887, when it was installed atop the south tower of this third pair. In 1923, a rotating fourth-order Fresnel lens made by Barbier, Bernard and Turenne of Paris replaced an earlier fixed lens, and that same year the north tower was moved to Eastham to become Nauset Light while the south tower remained as Chatham Light. The beacon, once powered by kerosene and turned by a weight-driven clockwork mechanism, was electrified in 1939, and later modernized again as its older lantern room and lens were removed in 1969 for preservation. Chatham Light remained safe when the ocean again broke through the barrier beach in 1987, and its modern beacon can be seen far out to sea. The fourth-order Fresnel lens represented a major advance in lighthouse illumination, using concentric prisms to magnify and project light far more efficiently than earlier lamps and reflectors.