They have been called lonely sentinels of the sea or symbols of romance: the lighthouses that helped sailors to navigate coastal waters. To the people who maintained the lights, romantic does not quite describe the job. And some of the sentinels were lonelier than others.

Use of lights to guide ships at night goes back to early civilizations. As soon as people took to the sea in boats, they needed navigational aids to guide them in darkness. It would not be until the 18th century, however, that lighthouses began to acquire the technology intended to make the lights more visible at sea. Early technology involved reflectors placed behind the light to help reflect the light into something close to a guided beam. At that time, the lights themselves were wicked, oil-burning lamps.

By the early 19th century, a French physicist named Augustin-Jean Fresnel (pronounced freh-nel’) invented a lens made of many glass prisms that refracted the light of the lamp, focusing it into a beam that carried a dozen miles or more to sea. The Fresnel lens used highly polished glass prisms that were held together in a brass rack. They came in many sizes, from a first-order lens taller than a man to relatively small lenses used for harbor and river lights.

The advent of electrical lights brought about another revolution in lighthouse technology. There was no need to carry cans of oil to the top of lighthouses, and the lights were both more dependable and brighter at greater distances. By the latter part of the 20th century, Fresnel lenses and powerful light bulbs gave way to beacon lights that were originally developed for air navigation.

Today Fresnel lenses still guide mariners into some harbors, and within harbors. Many have been preserved in their original lighthouses, and others, replaced by beacons, are in museums where people can see them up close. Some old Fresnel lenses were broken up over time. Technicians have researched both the kind of glass from which the originals were made and the processes by which they were cut and polished. A Fresnel lens in itself is a work of industrial art. The glass is very highly polished, and the prisms are fit together with a degree of precision that seems remarkable for mid-19th century technology.

Today lighthouses are not as necessary for navigation as they once were. Radio beacons, global positioning satellites, and radar have made ship navigation more reliable than ever.

Many lighthouses have been abandoned. Some have fallen into disrepair. Some have collapsed for lack of maintenance. Some have been awarded to states, towns, or museums and are open to visitation. Some are still active aids to navigation, still serving the purpose for which they were built. If modern technology fails, the old lighthouses remain to guide mariners.

For the keepers who maintained the lights, there was a daily grind of physical labor. Besides lugging cans of oil all the way up the steps of the lighthouse, they had to polish the prisms of the Fresnel lenses, clean the glass of the lantern room, whitewash or paint the exterior of the tower, and otherwise maintain their stations. For some located on offshore islands, tending lights could be lonely indeed. They had to row ashore in boats to get supplies, send kids to school, attend church, or get medical help. Some offshore islands allowed keepers of the lights to plant vegetable gardens or keep livestock. On others, ocean overwash in storms kept the rocks bare, and often threatened the lives of keepers. At any light station during storms, keepers were often called upon to help rescue the crews and passengers of ships that ran aground.

Besides being physically demanding and often lonely, the jobs of keepers were dangerous. Still, families of lighthouse keepers reflected on these times as good ones, and elements of romanticism color their memories. By the mid-20th century, the United States Coast Guard took over the care and maintenance of lighthouses from the old United States Lighthouse Service. For a time, keepers stayed on, working under the Coast Guard instead of the Lighthouse Service.

But slowly, lighthouses were automated and serviced by teams that were responsible for many lighthouses and that came out by helicopter or boat to maintain offshore lights. Today, both active and inactive lighthouses attract visitors. Some are open, and visitors climb the stairs to get dramatic views of the shoreline. Many include museums in the old keepers’ quarters. Several companies make figurines of lighthouses, and many other lighthouse-themed objects can be purchased.

Like much of our past, lighthouses have been romanticized well beyond any reality that existed for the hard-working, courageous keepers who climbed the steps lugging whale oil or kerosene, set out in storms to rescue wreck victims, or served in the tedium of isolation. At active lighthouses, the lights come on at dusk, shining out over the water to help guide mariners or perhaps to offer a reassuring signal that land is close by. They are not of our time, but they are in our time. They are more than romantic relics. And yet they keep their mystique.