Villanovan (and eventually Etruscan) sites show a close spatial association with young ultra-potassic volcanic rocks in both southern Etruria and Campania, a discrete cultural distribution that closely resembles the discrete occurrences of those unusual rocks. This association is probably due to the soil fertility that results from their weathering. In Etruria most sites line up along the margin of the volcanic terrane, which brought additional advantages for construction, defense, and resources. Trade for Elban iron ores with Campanian Greek colonies was also a factor enriching coast-facing sites. In Campania most Villanovan sites line up along the margins of coastal plains that had been fertilized by ultra-potassic volcanic ash falls. All three geologic features (the two volcanic areas and the iron deposits) are thought to have formed in the same tectonic environment, above a subduction zone where colliding tectonic plates melt at depth. Geologic factors apparently created environmental opportunities that each cultural entity in ancient Italy exploited differently.