This ancient elliptical construction dates from the first century BC, an it has been shaped out of the living rock. It was believed to be used for gladiatorial fights and circuses and was among the largest of buildings of this kind in Sicily - its measures are 140 to 119 m of external size and 70 to 40 m in the arena. There were two entrances to arena, each at one side of the longest axis and there was corridor at foot of steps for animals and gladiators with door to arena.
The rectangular place in the middle was to drain blood from fights and killings among other things. Gore stuff.
It is one of the first buildings at archeological site in Siracusa and here they didn't check tickets yet but I don't know whether is always free of charge. It is interesting architecture, still in quite good shape. There's something thrilling in the air if you imagine the horror scenes from Romans actually happening at the place where you're standing few milleniums later.