I was never interested in military history, and I’ve always thought of the ocean as a wild and natural place. But, when my then-boyfriend, now husband joined the Navy, I began to look at things a bit differently.

On and under those sometimes calm waters roam major vessels tasked with protecting our coasts. On a recent trip back to the island of Sardinia in the Mediterranean Sea, where my husband was stationed for a couple of years, I was reminded of how the now serene coast that draws tourists to its sparkling blue seas was once a formidable place to stay far away from. And, it got my thinking about the remarkable freedom that we have to enjoy our coasts when looking back at other eras when they were dangerous interfaces between cultures.

Sardinia has a particularly complicated history. While you might think of fishing as the primary industry and culture there, the island’s past has dictated otherwise. Invaders from every part of the surrounding world tried to capture and claim parts of the island from the Romans and Phoenicians, to the Arabs, Aragons, and Savoys.

Watchtowers along the coast remind us of that history, standing like sentinels from the past among the rocks. And, forts and fortresses from the first and second World Wars jut out above the landscape in their more modern, angular construction.

Now, you can look down from the turrets to see sailboats cruising the crystalline waters and sunbathers stretched out on the granite rocks below. But, this is a recent phenomenon. The ancient history of the island is focused inland, away from the coast, where the traditional shepherding people were safe from coastal attacks. Rather than sardines, they ate cured sausages, flat breads and aged cheeses that they could make and keep in the hills while tending their sheep.

In New England, the case is quite different, as people have relied upon resources from the oceans and built their settlements there for most of its human history. But, there is an amazing turn in the way that we think about our seas now versus a time not so long ago when there were armed men keeping watch throughout various conflicts.

For example, while now we might climb upon the weathered rocks around Fort Popham while taking a break from making sandcastles on a sunny, carefree Sunday, this spot was once a dangerous place that foreign ships might attempt to pass.

The first structure at Fort Popham was built during the Revolutionary War to protect the colonists. Then, the structure that we see today was built during the Civil War to protect the mouth of the Kennebec River from Confederates coming up to Augusta. It was used again in the Spanish-American war.

If you head up the hills above the park on the opposite side of the road, you will find Fort Baldwin, built in 1905 and manned in World War I. There is a battery and fire tower nestled in the now-quiet woods that provides a lovely view over Popham and the Kennebec River.

If you venture out into Casco Bay, you will find a great deal of military history from the World War II watch of Jewell Island, now frequented by boaters moored in the serene Cocktail Cove, to the stately hexagonal structure of Fort Gorges, built from 1858 to 1864 during the Civil War. Advances in military technology made the fort obsolete before it was ever manned, but the structure is on the U.S. National Register of Historic Places and protected as a park accessible only by boat.

And, if you travel up the rivers, there is more to be found, as well. I’ve always been fascinated by Fort Andross on the Androscoggin, which is better known now as the former Cabot Mill. But, a fort once stood there, built in 1688 as a trading post for fur trappers and as a garrison during King William’s War. Now, offices enjoy river views, as do visitors to the restaurants and the Winter Farmers Market that fill the spaces of the current building.

All of these structures are a part of our history and remind us of times when the coasts were dangerous places that required protection. While the aim of that protection was most likely not to save lovely beaches, spots for boating, and waterfront dining, but rather to ensure the safety of the people living in those areas at the time, we can certainly be grateful that one of the outcomes of this protection is now our ability to enjoy these places.

Rather than feel an ominous sense of history while taking a walk at the beach, I instead feel a deep respect and appreciation that comes from knowing the many points in our recent past when the safety of our coasts was in question.