During the twelfth and thirteenth centuries, the medieval world began to experience a series of changes. An increase in population began to be seen as a result of a notable increase in agricultural production mainly due to:
- Acquiring new lands.
- The appearance of the landfill plow replacing the old Roman plow.
- The horse begins to be used as a draft animal instead of oxen.
- The invention of new agricultural tools such as scythe, collar and nail horseshoe.
- The wind and water mills were perfected.
- Improvements in irrigation techniques, introduced mainly by the Arabs (Ferris wheels, ditches).
- Introduction of new crops such as citrus, saffron, eggplant, sugarcane, etc., most of them brought to the land by the Arabs.
- Better adaptation of cropping systems.
As a result of this greater production, the first agricultural surpluses appeared, which soon began to be commercialized, enabling the approach of the countryside to the city. This made possible to expand old cities and the creation of new ones.
Other causes for which there was a strong displacement of population from the countryside to the city, were the rejection of the extreme servitude to which the peasants were subjected by the feudal lord as well as the aspiration to have a trade and the desire of the kings of expand their territories and their authority, founding royal villas (new villas or free villas), with the settlement of people of all conditions, who depended directly on the king. He freed them from the feudal laws and granted them franchises.
These new cities were surrounded by a defensive wall, equipped with watchtowers and drawbridges at their doors that prevented the passage into the interior. Inside they held fairs and markets where important commercial transactions were carried out.
Markets were held once or several times a week and traded primarily with agricultural products; the fairs were generally annual, with a fixed date, and they were traded with cattle and tools. Some fairs reached international fame for the importance of their exchanges.
Kings and city councils tried to protect merchants by putting serious penalties on crimes committed in markets and fairs; Thus, for example, the use of weapons in markets was prohibited.
The transfer of goods favored the appearance of commercial routes, both land, and sea, as well as groups of merchants and merchants, as was the case of Hansa in the North and Central Europe, which protected and controlled the business of its associates.
To favor commercial exchanges, the bank created two new financing systems: credit sale and the bill of exchange.