Most Countries that maintained a coastline, needed some form of defensive measures to protect themselves from seaward attacks. The development of Sea Forts are as old as their need. Especially when many Nations began to colonize The New World and other points in The World (15th Century onward), many Sea Forts began to develop. Spain and France were among the forerunners of many Sea Fort advances in construction. Mostly built from stone and shale sand mortar (for an amazingly strong reinforcement), these structures were designed to withstand cannon assault from the sea. Therefore, many examples were large structures that featured increased and robust defenses facing that direction. Many Sea Forts were also constructed at Harbor and Port entrances to provide defense against enemy shipping. Their sheer size also afforded large garrisons of soldiers or Marine forces. In many cases, when possible – Sea Forts were constructed on plateaus and cliff tops to assist with range (of artillery) and observations. Star and Quadrangular designs were also extremely popular – utilizing Outwork, Horn Work and Crown Work systems as part of their construction. Due to the time and resources spent on their construction, many fine examples of Sea Forts have existed (and were used) well into the 20th Century.