Complex sentence: The collegiate church was constructed in the Flamboyant style at the end of the 15th century, was made a cathedral in 1822, and a neo-Gothic nave, designed by the architects Lassus and Millet, was added at the end of the 19th century.
Split into simpler sentences: The collegiate church was constructed in the Flamboyant style at the end of the 15th century. To this a neo-Gothic nave, designed by the architects Lassus and Millet, was added at the end of the 19th century.