Originally the site of the Forum had been marshy ground, which was drained by the Tarquins with the Cloaca Maxima. Because of its location, sediments from both the flooding of the Tiber River and the erosion of the surrounding hills have been raising the level of the Forum floor for centuries. Excavated sequences of remains of paving show that sediment eroded from the surrounding hills was already raising the level in early Republican times. As the ground around buildings began to rise, residents simply paved over the debris that was too much to remove.