Captain Lemuel Moody organized the Portland Observatory in 1807 atop Munjoy Hill, and its signal tower rises over Congress Street above you. It is the only known surviving tower of its type in the United States, and it still embodies its original purpose: using a telescope and signal flags to create two-way communication between ship and shore, often several hours before an incoming vessel reached the docks. Look up — the octagonal tower rises 86 feet (26 m) and contains seven stories, its shape chosen to lessen wind pressure.
In times of war it kept watch; during the War of 1812 it served as a watch tower. Today it is preserved as a museum managed by Greater Portland Landmarks, and in 2006 it was honored as both a National Historic Landmark and a National Historic Civil Engineering Landmark. Imagine merchants on the wharfs, alerted in advance by signals, and mariners out on the deep harbor that is sheltered by numerous islands, with ships not directly visible from the docks.
The observatory solved that problem by sitting where sea and city meet. Notice the harbor and the islands that shelter it.