Complex sentence: He was born at Muret, and entered the École Polytechnique in 1821, passing on to the engineer school at Metz, becoming lieutenant in the Engineers Corps in 1827 and captain in 1833.
Split into simpler sentences: He was born at Muret and entered the École Polytechnique in 1821. Niel entered the engineer school at Metz, became lieutenant in the Engineers Corps in 1827, and captain in 1833.