By the eleventh century, Chinese texts of the Song dynasty — most famously Shen Kuo's Dream Pool Essays of 1088 — describe a magnetised iron needle used to indicate direction, building on earlier knowledge of lodestone. By the twelfth century the device was being used to guide ships, and a comparable navigational compass appears in the Mediterranean around 1190. The instrument let mariners hold a course when neither coastline nor stars were visible. It was steadily refined with the compass card and, later, the gimbal.
The magnetic compass freed long-distance trade and exploration from dependence on the coast and clear skies, extending the sailing season and the open-water routes that fed the growth of port cities across maritime Asia and Europe.