The distinctive sequence enables the lighthouse not only to warn mariners but also to help identify their locations.

A light buoy was constructed near the rock outcropping to warn mariners about the island.

The light thus had two purposes: (1) it marked a turning point; and (2) it warned mariners away from the rocks and shallows.

They warned mariners about a dangerous shoal.

For 67 years the light served to warn mariners about the shoals off the point.

A bell was established at Roche's Point in 1864 to warn mariners in poor visibility.

It marks the entrance to the inlet and warns mariners of the extreme tidal turbulence.

When lighthouses were built to warn mariners away from the shoals, they saved many lives.

Lighthouses warn mariners about prominent rocks and peninsulas.

They often warn mariners of specific dangers such as rocks and reefs or bridge abutments.