Complex sentence: The citadel was begun in the 9th century with the foundation of the city, has been reconstructed and renovated many times since then, and most recently was an administrative center for the French Foreign Legion.
Split into simpler sentences: The citadel was built in the 9th century with the foundation of the city. The Citadel has been reconstructed and renovated many times since its constructio and most recently was an administrative center for the French Foreign Legion.