The locality of Trelleborg has never been completely forgotten. Most of its earthworks were visible right up until the site was excavated, and the circular inner rampart can clearly be seen on maps from the 17th century and onwards. Trelleborg was first recognised as a Viking fortification when the National Museum commenced excavations in 1934, led by the archaeologist Poul Nørlund who also excavated the Scandinavian cemetery at Herjolfsnes in Greenland and undertook a number of other large excavations.
The excavation was initiated after a local motorbike club rented the area in 1933 and planned to convert it into a motocross track. What had been originally envisioned as a small-scale investigation ended up lasting 9 years, up until 1942. By this time most of the area had been investigated, and the outer defences had in 1936 been discovered on an aerial photograph. Up until then, the outer earthwork had not been known as it was no longer visible in the landscape.
All the post holes were marked with cement blocks, which today still indicate the locations of the buildings in the fortress area. In 1941-42 work began on a reconstruction of one of Trelleborg’s characteristic long houses. This project was led by Poul Nørlund and the architect C.G. Schultz. The house is thought to be the world’s first scientifically based reconstruction of a prehistoric building. It was thoroughly renovated at the start of the 1980s, and despite the fact that it has since its construction been shown to be incorrect in certain respects, the house still gives a good overall impression of the appearance and construction of long houses.