A Scheduled Ancient Monument and our most historic site. Devil's Dyke is an impressive earthwork. Even today, more than 2,000 years after its construction, it is up to 40 feet (12 metres) deep. Sir Mortimer Wheeler excavated the dyke in the 1930s and suggested it was the site where Julius Caesar defeated the resistance led by the local Catuvellauni tribe under Cassivellaunus. It is a very significant Iron Age monument and partly responsible for St Albans Museum's reference to Wheathampstead as "The First Capital".