What was the Roman Colosseum made out of?

The Colosseum was constructed from over 100,000m3 of travertine stone, held together by 300 tons of iron clamps. It was extensively damaged by earthquakes and much of the stone and ironwork was robbed or re-used to build houses. The seats were originally stone but later changed to marble. There would also have been an overhanging canopy all round the arena, made of wood and cloth, much like the stadiums of today, to provide shade and shelter to the spectators, however both have long since disintegrated.