 The Sweet Track is an ancient causeway in the Somerset Levels , England . It was built in either 3807 or 3806 BC and was the oldest timber trackway discovered in Northern Europe until the 2009 discovery of a 6 @,@ 000 @-@ year @-@ old trackway in Plumstead , London . It is now known that the Sweet Track was predominantly built over the course of an earlier structure , the Post Track . 
