Trade and its evolution was a necessary part of both economic expansion as well as the exchange of new ideas. Trade's development depended on the tools of writing and domestication: writing to record deals and domestication to provide transportation. Previously, the uncertainty of lawlessness or the encumbrance of barter hindered the exchange of goods. However, writing provided contracts to reassure business people, and the development of pack animals made distant travel a reality. Soon, merchants were plying their neighbors for the best prices in the land.