Galleons were a natural evolution of the Caravel and Carrack (also called "Nao"). A revolutionary lowering of the foc's'l (forecastle) gave an unprecedented level of stability in the water - leading to a faster, more maneuverable vessel.
The galleon was powered entirely by sail - usually 3-5 masts. They were used in both military and trade applications. In fact, galleons were so versatile that a single vessel may have been refitted for war- and peace-time roles several times during its lifespan.
Galleons were constructed from oak (for the keel), pine (for the masts) and various hardwoods for hull and decking. Hulls usually were constructed in carvel-building style. The expenses involved in galleon construction were enormous. Hundreds of expert tradesmen (including carpenters, pitch-melters, blacksmiths, coopers, shipwrights, etc.) worked day and night for months before a galleon was seaworthy. Due to this, galleons were often funded by groups of wealthy businessmen who pooled resources for a new ship. Therefore, most galleons were originally consigned for trade, although capture by rival nations usually put the galleon into military service.
The most common gun used aboard a galleon was the demi-culverin, although gun sizes up to demi-cannon were possible.
Due to extensive time often spent at sea and poor conditions on board, advanced rigging systems were developed so that the vessel could be sailed home by an active crew a fraction of the size aboard at departure.
See also: Galley