Even in the Middle Ages, when industry was backward and most of the exchanges were carried on by barter, there were accumulations of capital in the form of gold and silver. Kings levied taxes and maintained treasuries; and borrowed great sums with which to carry on war, to make crusades, or to provide dowries for their children. Merchants and traders, too, often needed more ready money than they themselves possessed. Consequently, there grew up a class of men, confined largely for religious reasons to the Jews and the Lombards, who, seeing the advantages of making loans, kept their wealth liquid - that is, in the form of gold and silver. Obviously, they were compelled to take measures for protecting themselves against thieves. Soon, we may believe, their neighbors who had surplus funds of their own began to leave their money with these lenders for safe-keeping.