Archaeological excavation at Seahenge began October 1998, under site director Mark Brennand of the Norfolk Archaeological Unit. It proved a difficult site to excavate. Sea tides restricted trial trench excavating work to between one and four hours per day. A Dendrochronological sample extracted from the stump was sent for analysis at Sheffield University. By January 1999, preliminary results indicated a Bronze Age monument. Despite projected expense, English Heritage decided full excavation would be worthwhile, because the site had begun to suffer from erosion. Sections of wood had been exposed to corrosive oxygen and salt brine after millennia protected in the mud.