What is the width of the Colosseum in meters?

The Colosseum is 156 meters wide.

Its plan is an ellipse rather than a circle, so it has two principal dimensions: about 189 meters along its longer axis and 156 meters across its shorter axis. The width measures the building from one side of the ellipse to the other, not the width of the central arena.

That distinction explains a frequent quiz mistake. The arena itself was much smaller, approximately 83 meters long by 48 meters wide. The broad space between the arena wall and the exterior contained the podium, tiered seating, passageways, stairways, service areas, and structural supports needed to move tens of thousands of people.

The amphitheatre’s huge footprint helped make it the largest ancient amphitheatre ever built. It stood roughly 48 meters high and had a perimeter of about 545 meters. Roman builders used travertine limestone, tuff, and brick-faced concrete, combining heavy masonry with an extensive system of vaults and corridors.

Some references round the dimensions differently, but 156 meters is the standard stated width for the completed Colosseum. The figure refers to the exterior structure, not the arena floor.