- "He who commands the sea has command of everything."
One of the great achievements of early civilizations, Sailing develops the means to travel the seas by building Triremes, and to access sea resources by building Work Boats. For now, your vessels can only travel in coastal waters.
Sailing also enables access to the second Trade unit - the Cargo Ship - and to your second Trade route.
Sailing is the art of harnessing the power of the wind to move a boat over the water. To be successful, sailing required the mastery of a number of diverse skills. First, the culture must be able to construct a seaworthy craft. Second, they must be able to construct some sort of sturdy sheets (sails) which can catch the wind and transmit its energy to the hull. Third they must be able to build the various ropes and cleats and pulleys used to control the ship's sails, and finally they must be able to successfully navigate the vessel from point to point without getting lost or capsizing or suffering some other misfortune.
The earliest recorded evidence of watercraft can be found in illustrations in Egypt which date from around 4,000 BC. As a riparian (river-based) civilization, the Egyptians were excellent sailors. Many of their vessels contained both oars and sails, the former being used when the winds weren't strong enough or weren't coming from a favorable direction.
By 3000 BC the Egyptians were venturing out into the Mediterranean Sea in their vessels, steering the lengthy journey across the open water to Crete and later Phoenicia. The Egyptians also sailed down the coast of Africa, looking for knowledge, trade and treasure.
The earliest warships - biremes and triremes and the like - were powered by oar and sail and possessed rams or beaks on their prows. During battle the helmsman would attempt to ram the enemy vessel at high speed, while avoiding the enemy's earnest attempts to do the same thing. Some vessels were equipped with archers to fire at enemy craft from longer distance, while others had soldiers aboard; these vessels sought to come alongside the enemy craft so that their soldiers could board the other ship and take it by storm.
The Greeks - especially the Athenians and the island colonies - were masters at naval warfare. One of the reasons that they were able to defeat their much larger and more powerful neighbor, Persia, was that the Athenian navy dominated the Aegean Sea and thus constantly threatened the Persians' increasingly lengthy supply chain.