In 1723 Bach moved to Leipzig to take the job of "Cantor" at the St Thomas Church, a very large church in the town. As "Cantor" he was in charge of all the music, both at St Thomas and at another church nearby. He also had to compose music for the town. It was an excellent job, and more secure than being at a court. The schools were good for his sons. Bach stayed in Leipzig until his death. He loved his job most of the time and worked very hard. He composed many cantatas for the church services. These services were very long, lasting about three hours. Many of the cantatas he wrote last about 30 minutes, and that was just one part of a service! He had assistants to play the organ. Bach himself directed the choir and the orchestra. There were probably 16 singers in the choir and 18 players in the orchestra. He wrote the "St Matthew Passion" and the "St John Passion". Both these works, which are very long, tell the story of Jesus dying on the cross. They are among the most famous pieces of music ever written. He also wrote cantatas for special occasions such as weddings or funerals.