‘Stadtluft macht frei’ (‘City air makes you free’) is a popular German saying, referring to a principle of law in place in Europe during the Middle Ages. This one would enable a serf living unfree under feudalism to become free from their lord, in a city, after a period of one year and one day. This increased the migration of medieval people seeking freedom from the feudal territories to the cities from the 11th century onwards.
Because of that freedom, cities became a centre of trade, gathering merchants, entertainers and much more, and offering a large variety of products and services. This made the cities vibrant and prosperous, with its inhabitants enjoying better life conditions than on the feudal territories.