The Adena began constructing large earthwork mounds around 600 BCE. Illinois researchers discovered the remains of several earthwork mounds. There are three related types of Neolithic earthwork that are all sometimes loosely called henges. Part of his defences used the ancient Belgic earthwork known as Beech Bottom Dyke. Five forts of earthwork or rifle pits were constructed, and a solid defense was prepared. The general term, "mound builder", covered their shared architectural practice of earthwork mound construction. This ancient earthwork mound and site, built ca. Its definition included remnants of four other nearby earthwork and mound systems. Hideyoshi also built earthwork walls called encircling the city. The castle was a small fortified manor house, built to replace an earlier earthwork. The site covers an area of over within a polygonal earthwork. It is transected east and west by the ancient earthwork called Grim's Dyke. Although superseded by their stone successors, timber and earthwork castles were by no means useless. The "Broken Circle" earthwork was built in a quarry lake 10-to-15 feet deep. There are a number of earthwork step pyramids within North America.