From the earliest times,man has been interested in art.People have often worked together to collect and save the world's art treasures. Fine art treasures from many countries are kept in an art museum called the Louvre in Paris,France.The works of art have been collected by the people of France over many centuries. The Louvre has not always been a museum.The first building was a fort .In 1190,it was the king's castle with high walls and a round tower.It had a _ to keep out his enemies. Over the years,the number of buildings around the castle grew.By 1350,the castle was no longer needed as a fort.The Louvre became a palace home for French kings and queens. During times of peace,new treasures were brought in.During days of war,many treasures were stolen,and the buildings were damaged. When Francis I became king of France in 1515,he brought in artists from many countries.One of the artists was Leonardo da Vinci from Italy.Da Vinci's "Mona Lisa" is the best known painting in the museum today. In 1793,the Louvre became a public museum,just as it is now.It is a place where art treasures have been saved for everyone to enjoy. On the whole,this passage is mainly about  _  .
an art museum called the Louvre an Italian artist named Leonardo da Vinci a king of France named Francis I the best known painting in Louvre