Complex sentence: The Théâtre du Châtelet is a theatre and opera house in Paris, France, one of two theatres built on the site of an old fortress by Gabriel Davioud at the request of Baron Haussmann between 1860 and 1862.
Split into simpler sentences: The Théâtre du Châtelet is a theatre and opera house in Paris, France. One of two theatres built on the site of a "châtelet", a small castle or fortress, it was designed by Gabriel Davioud at the request of Baron Haussmann between 1860 and 1862.