Beneath Our Feet: The oldest surviving charts depicting the Mediterranean Sea date to the 13th century; however, these earliest maps created by mariners for navigational purposes did not reflect features beneath the surface of the water. It was not until the production of the first Dutch sea atlas in the late 16th century that nautical charts began recording bathymetric (underwater depth) information. By the late 18th century, mariners had developed established methods for recording underwater depths, landforms and hazards, as seen on this chart of Boston Harbor. Soundings – water depths at specific locations – are represented by numbers indicating fathoms here, while shoals and sandbanks are illustrated with stippling.