Wales was a rich source of mineral wealth and the Romans used their engineering technology to extract large amounts of gold, copper, and lead, as well as modest amounts of some other metals such as zinc and silver. When the mines were no longer practical or profitable, they were abandoned. Roman economic development was concentrated in southeastern Britain, with no significant industries located in Wales. This was largely a matter of circumstance, as Wales had none of the needed materials in suitable combination, and the forested, mountainous countryside was not amenable to development.