The contours of the ancient stadium, first built in the 6th Century B.C., are still visible in what is now a park in the shadow of the Palatine. Circus Maximus was primarily devoted to chariot races and was used for this purpose until around 550 A.D. The stadium could seat up to 150,000 people. Originally built of wood, it burnt down twice, on the second occasion starting the great fire when the Emperor Nero was said to fiddle while Rome burned. It was in one of the tunnels here that Caligula met his end. Excavations began in April 2009 at the east end of the circus and are likely to go on for some years.