Colosseum is about 23 times smaller than Holy See (Vatican City).

Holy See (Vatican City) is approximately 0 sq km, while Colosseum is approximately 0.019 km² (0.0075 sq mi), making Colosseum 4.39% the size of Holy See (Vatican City).
Tip: This to-scale comparison of Holy See (Vatican City) vs. Colosseum uses the Mercator projection, which distorts the size of regions near the poles.
Our free app, MapSize by MyLifeElsewhere — compare any two places, to scale on your mobile device.