The use of money grew up in the city. The density of population made it easy, the growth of wealth made it possible, and the nature of the exchanges made it necessary. Whereas the relation of landlord and serf under the renting contract continues from year to year, the relation of the buyer and seller of shoes, hats, etc., in the city, is temporary, these things forming only a part of man's economic needs. Barter with a particular individual is much more inconvenient if exchange is only occasional than where the contract is a continuing one, and there is an annual balancing and settlement of accounts. So, as city industry and commerce grew the use of money increased, both in small neighborhood trade and in the larger transactions with distant countries; and thus the business methods of the cities grew into sharper contrast with those of the rural districts. [Sidenote: Money loaned and borrowed in cities] 5. _The loan and hire of wealth in medieval cities came to be expressed as a money loan._ The loan of money and of other wealth expressed in terms of money, began in the cities. The use of money and the expression of the value of things in terms of money was common there throughout the Middle Ages. Moreover, as the movable forms of wealth multiplied, the agreement to return borrowed wealth in kind became impossible in cities; the loan in terms of money became the only practicable thing. A merchant embarking on a trading expedition must have such a number and variety of goods, that he finds it both very difficult to rent them and wasteful in time to enumerate them and return them in like kind. It therefore became usual to make a loan either of the things expressed in terms of money, or of money with which to buy the things, thereby reducing to a single, simple, easily interpreted contract, the indebtedness which the borrowing of a thousand different things occasioned. [Sidenote: The medieval opposition to loans at interest]