Originally an island that was used for agriculture, in 1928 Norsk Hydro decided to locate a new artificial fertilizer factory there, Hydro Porsgrunn, and in just 16 months both this factory and a shipping port for Norwegian saltpeter (calcium nitrate) were built. In the process, the narrow sound between the island and the mainland was mostly filled up, thus transforming the island to a peninsula. The reason Hydro wanted to establish itself in the Grenland region was the proximity to limestone, one of the necessary components in the fertilizer, Calcium nitrate. Norsk Hydro had previously had to build its fertilizer plants in Notodden (in 1907) and Rjukan (in 1909) because technology at that time didn't allow for efficient transport of electricity long distances from the power plants to the place of use. But in the 1920s technology had developed and it was possible to locate the plants close to the natural resources instead of close to the hydro electric power plants, that were located in the mountains in Northern Telemark.