(though not the same status), not all people were equal. Immigrants into a village or city had no political rights and were called the Hintersassen. In rural areas, they had to pay for their use of the common lands. They were granted equal rights only when they acquired citizenship, which not only was a question of wealth (for they had to buy their citizenship), but they also had to have lived there for some time; especially in the rural areas. The cities followed an expansionist territorial politics to gain control over the surrounding rural areas, on which they were dependent, using military powers or more often more subtle means such as buying out, or accepting as citizens the subjects (and thereby freeing them: "Stadtluft macht frei"—"city air liberates") of a liege lord. It was the cities, now, that instituted reeves to manage the administration, but this only sometimes and slowly led to a restriction of the communal autonomy of the villages. The peasants owned their land, the villages kept administering their commons; and the villagers participated in the jury of the city reeve's court. They had, however, to provide military service for the city, which on the other hand included the right to own and carry weapons. Basel became the center of higher education and science in the second half of the 15th century. The city had hosted the Council of Basel from 1431 to 1447, and, in 1460, a university was founded, which eventually would attract many notable thinkers, such as Erasmus or Paracelsus. Economy The population of the cantons numbered about 600,000 in the 15th century and grew to about 800,000 by the 16th century. The grain production sufficed only in some of the lower regions; most areas were dependent on imports of oats, barley, or wheat. In the Alps, where the yield of grains had always been particularly low due to the climatic conditions, a transition from farming to the production of cheese and butter from cow milk occurred. As the roads got better and safer, a lively trade with the cities developed. The cities were the marketplaces and important trading centers, being located on the major roads through the Alps. Textile manufacture, where St. Gallen was the leading center, developed. Cheese (esp. Emmentaler and Gruyère) also was a major export item. The exports of the Swiss cities went far, into the Levant or to Poland. In