The covered passageways, also known as "porches", made it easier to access the inner courtyards. Today, you can use them to go from street to street, from ramparts to square, from monument to monument.
A little history:
In 1825, the "Café des Pauvres" was set up in the passage between rue de la Boucherie and rue Jean Roussat. People entered through the courtyard in the centre of this porch "without being seen by the public"; "both sexes were admitted" but the mayor, having learnt "that orgies were continually taking place there", had it closed in 1829.
Les passages couverts