Basle the second largest city in northern Switzerland, on the River Rhine. or Basle French Bâle City (2000: city, 166,558; metro. area, 402,387), northwestern Switzerland. It straddles the Rhine at the point where France, Germany, and Switzerland meet. It was originally a settlement of the Celtic Rauraci tribe. Its university, the first in Switzerland, was founded by Pope Pius II while attending the Council of Basel (1431-49). In 1501 Basel was admitted into the Swiss Confederation. When Desiderius Erasmus taught at the university (1521-29), the city became a centre of humanism and of the Reformation. Primarily German-speaking and Protestant, it is an important trading and industrial city and river port