 Tarr Steps are a prehistoric ( circa 1000 BC ) clapper bridge across the River Barle , about 4 km ( 2 @.@ 5 mi ) south east of Withypool and 6 km ( 3 @.@ 7 mi ) north west of Dulverton . The stone slabs weigh up to 5 tonnes apiece and the bridge has been designated by English Heritage as a grade I listed building , to recognise its special architectural , historical or cultural significance . There is little evidence of Roman occupation apart from two fortlets on the coast . Lanacombe is the site of several standing stones and cairns which have been scheduled as ancient monuments . The stone settings are between 0 @.@ 3 metres ( 1 ft 0 in ) and 0 @.@ 65 metres ( 2 ft 2 in ) high . A series of Bronze Age stone cairns are closely associated with the standing stones . 
