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Beacons / Monuments / Spindles
A "spindle" is a fixed marker to indicate a hazard to navigation (such as a rock which couldn't be seen at high tide). It serves the same purpose as a channel buoy, a "light beacon," or a “monument,” to warn vessels away from dangerous places or stretches of coastline. Spindles are usually iron rods with some sort of geometric object (round, flat, or triangular) on top, brightly painted (usually red) for visibility. Monuments, like the ones you see in Lane’s depictions of Half Way Rock or Norman’s Woe Reef, were made of stone and look like stumpy obelisks—or grave monuments. They were also essential as reference points for the early coastal surveys in their efforts to make more accurate charts.
In Castine, the notable square monument in the center of the harbor marked Hosmer's Ledge.