In the next century the superimposed stern castle is gradually absorbed into the sheer of the ship so that it formed a genuinely sheltered cabin. As the needs of war developed the castles also got higher and more bulky. A thirteenth century cog ex Greenhill. Deutsche Schiffahrtsmuseum 1985. IJNA 16.1 P69.
Cogs appear also in the literary evidence.
In the English sources Matthew Paris, Thomas Walsingham and Matthew of Westminster all speak of the cog as being Northern Boat, but the word cog was in use at least as early as the eleventh century. The present Flemish word for boat is Coche, and the Welsh word Cwch meaning boat betrays the Celtic origins from which the Cog derived. Thomas Walsingham speaks of great cogs in 1331 with three decks and over 500 crew and soldiers. In the fifteenth century chroniclers speak of cogs of 1500 tons, but they may either exaggerate or confuse the cog with other types. Ships like this couild go almost anywhere in the known world but the extra beam required to give greater capacity put a considerable strain on the clinker construction techniques of the Northern European shipbuilders.