Complex sentence: He is also the patron of the city of Groningen, and it's Martini tower and Martinikerk (Martin's Church) were named after him, the city is often named the Martini-city.
Split into simpler sentences: He is also the patron of the city of Groningen, and its Martini tower and Martinikerk (Martin's Church) were named after him. The city is often named the Martini-city.