The outer wall is estimated to have required over NUMBER@1 cubic meters -LRB- NUMBER@2 cu yd -RRB- of travertine stone which were set without mortar held together by NUMBER@3 tons of iron clamps .

The outer wall was made from about NUMBER@1 cubic meters -LRB- NUMBER@2 cu yd -RRB- of travertine stone . This was held together by NUMBER@3 tons of iron clamps .
