There are two main reasons why boat windows are round. They are easier to seal and, above all, more resistant to the high pressure that water exerts on them. This is because living corners are places where tensions are naturally concentrated, weakening the structure as a whole. This is also why aircraft windows are small and round; high pressures are better distributed in curved shapes, reducing the likelihood of cracks or breaks.
In architecture, circular openings are quite old. The Oculus, a type of circular window, has been a feature of classical architecture since the 16th century. Also known by the French expression oeil de boeuf (bull's eye), circular or semi-circular openings are formed from the construction of masonry arches, which allow for the creation of openings only by locking the constitutive pieces. Over time and following the incorporation of new technologies and development of construction knowledge, creating rectangular openings in buildings has become easier, more efficient, and cheaper than creating round ones. However, these circular windows still continue to figure in a multitude of projects.