[4][5] The island features a prominent black and white stucco-covered wood pyramidal daybeacon, or channel marker, resting atop a granite base[6] erected by the Boston Marine Society in 1805.

Reaching a height of approximately 20 feet (6.1 m),[3] the beacon serves as a Federal aide to navigation, warning passing ships of one of the harbor's most hazardous shoals.

The pyramid's hollow innards comprise a mortise-and-tenon wood structural system supported by cross-members radiating from a central column.

With no action from Congress the Commonwealth of Massachusetts purchased the island and authorized $3,000 in state funds for the building of the wall and the beacon.

By 1832, the U.S. government purchased the island and started to build the stone platform and wood pyramid, which was struck by lightning and burned in 1841, then reconstructed.