Balt Moor Wall is an earthwork and listed scheduled ancient monument in Lyng, Somerset, England, situated on the Somerset Levels to the northwest of the River Tone. The site contains the remains of a section of medieval causeway, which now forms a raised embankment between 6 metres (20 ft) and 10 metres (33 ft) wide and up to 2 metres (6 ft 7 in) high. The structure, which English Heritage refers to as "a rare example of medieval engineering", appears to have been built to protect the from the flooding of the River Tone in the Athelney-Lyng gap.