The Cirque de Gavarnie is compared to what oval amphitheatre built of concrete and sand is the largest amphitheatre ever built?
Cirque de Gavarnie: The Cirque de Gavarnie is a cirque in the central Pyrenees, in south-western France, close to the border of Spain. Cirque de Gavarnie:  It was described by Victor Hugo as "the Colosseum of nature" due to its enormous size and horseshoe shape causing a resemblance to an amphitheatre. Colosseum: The Colosseum or Coliseum ( ), also known as the Flavian Amphitheatre (Latin: "Amphitheatrum Flavium"; Italian: "Anfiteatro Flavio" ] or "Colosseo" ] ), is an oval amphitheatre in the centre of the city of Rome, Italy. Colosseum:  Built of concrete and sand, it is the largest amphitheatre ever built.
Colosseum