During the Bronze period Halle was a seat of wealth, and the large amount of copper found here suggests that the production of salt had begun here before the close of Neolithic times. Hoernes says that the production of salt at Hallstadt, a source of great wealth and luxury during the earliest Iron Epoch, and of no small extent during the Bronze period, had its beginnings in Neolithic days. The value of salt in trade or barter can hardly be overestimated. A very small amount of gold, mostly in the form of beads, has been found in the Neolithic monuments of France erected at the very close of this period. Occurring native in small nuggets in the beds of streams and rivers of many parts of Europe, its color and malleability must have attracted the notice of the searchers after new material for implements. Large nuggets were found in Spain at a much later date with callais, a mineral resembling turquoise, which occurs from Portugal to Brittany.[105] Objects of copper were found by Pumpelly at Anau contemporary with the appearance of turbary sheep, about 6000 B. C.[106] It appears in Egypt perhaps 1,000 years later. We find traces of it in the oldest city of Troy (Hissarlik). It may well have entered southeastern Europe by way of Troy, or northward from Greece through the Balkan Peninsula to the Danube valley. A more westerly route lay open through Italy, or the islands west of it, into Spain. Native metallic copper seems to fail in Europe proper, but mines for ore were opened in Tyrol, and probably elsewhere, before the end of the period.