The Ambrosian Diocese takes its name from the patron, the Bishop and Saint Ambrose (334-397), and it is one of the largest in the world, not so much for its area (4,250 sq. km.), but for the number of priests, nuns and monks, structures and works found throughout its territory, and coordinated by the Archbishop of Milan.
The Diocese once had more extensive boundaries than it does now, but over the centuries these have been downscaled: in the last 400 years, in fact, 43 parishes have been transferred to the Diocese of Bergamo, 55 to Lugano, 20 to Novara, 12 to Pavia, 2 to Como and Casale Monferrato, and 1 to Piacenza.
The Diocese is divided into seven easily-managed Pastoral Zones (I - Milan; II - Varese; III - Lecco; IV - Rho; V - Monza; VI - Melegnano; VII - Sesto S. Giovanni), which, in turn, include 74 Deaneries.
Each Deanery comprises several parishes: a group of Deaneries will compose a Zone, which is led by an Episcopal Vicar who is appointed by the Archbishop. The Deaneries are managed by Deans who are chosen from the top three elected by the clergy of each Deanery.

The Diocese of Milan
Parishes of the Diocese