Gudfred. Size The Danevirke is about long overall, with a height varying between . During the Middle Ages, the structure was reinforced with palisades and masonry walls, and was used by Danish kings as a gathering point for Danish military excursions, including a series of crusader raids against the Slavs of the south Baltic. In particular, the 12th-century King Valdemar the Great reinforced parts of the Danevirke with a brick wall, which enabled a continued military use of this strategically important structure. The reinforced parts of the structure are consequently known in Danish as Valdemarsmuren (lit: Valdemar's wall). Stages in the building of the Danevirke Danevirke 1 – Hovedvolden ("the main rampart"), Nordvolden ("the north rampart"), Østervolden ("the east rampart")The first Danevirke was built in five stages, starting about 650, according to carbon-14 dating. The first three stages were simple ramparts of soil, and the fourth stage was a palisade rampart with heavy timber front, built in 737. In the final stages the timber palisade was reinforced with a heavy stone wall around the timber. Work is said to have been started by Angantyr, and continued by Siegfried, and ended by Guðfrið according to annales in 808. Hovedvolden: From Rejde Å (now called Rheider Au) to a small lake called Dannevirke Sø. It was the main segment of the Danevirke. About 2 m high and 12 m wide. Nordvolden: From the northeastern side of Dannevirke Sø, and further north about 7 km. Østervolden: About 3.3 km long, and protecting Schwansen. A 900 m long submerged construction in Slien. Danevirke 2 – Kovirke ("cow-work")/Kograben ("cow-moat" or "district moat")Built either by Guðfrið or by Harald Bluetooth (if it is the work mentioned as newly made in the Frankish royal annals in 808, then Harald did not build it) it stretched from the Rheide Å about 7 km to a southern extension of the Schlei bay which is now a lake called Selker Noor. Its palisade was about 3 m high, and was a little more solid than that on the first ramparts. The bank of earth behind the palisade was about 2 m high and 7 m wide. It had a V-shaped moat, 4 m wide and 3 m deep.The construction period of this rampart would have been some time between 770 and 970. Danevirke 3 – Hovedvolden/Hauptwall/"main rampart", Krumvolden/Krummwall/"curved rampart", Buevolden/Bogenwall/"bow rampart"), Dobbeltvolden/Doppelwall/"double rampart", Forbindelsesvolden ("the connecting rampart")/Margarethenwall ("Margret's rampart")Hovedvolden was