Read the extract given below and answer the question that follows:

The Silk Routes are a good example of vibrant pre-modern trade and cultural links between distant parts of the world. The name ' Silk Routes ' points to the importance of Westbound Chinese silk cargoes along this route. Historians have identified several Silk Routes, over land and by sea, knitting together vast regions of Asia and linking Asia with Europe and Northern Africa. They are known to have existed before the Christian Era and thrived almost till the fifteenth century. But Chinese pottery also travelled the same route, as did textiles and spices from India and Southeast Asia. In return, precious metals - gold and silver flowed from Europe to Asia. Trade and cultural exchange always went hand in hand. Early Christian missionaries almost certainly travelled this route to Asia, as did early Muslim preachers a few centuries later. Much before all this, Buddhism emerged from eastern India and spread in several directions through intersecting points on the Silk Routes.

The Silk Route was never used for which of the following?