The Burj Khalifa _is_ a certain marvel. Most interesting I find the way they conceived the foundations as a clever and effective system of friction. I must recommend the documentary hosted by Richard Hammond for the "Big!" series (2020), episode Tallest Building On Earth.

Probably in terms of occupied surface it is not that much, but some find it helpful when a construction (even "comparatively modest") is conveniently placed in an open air museum as big as a city.

-- the very numbers reported here introductorily estimate a maximum of 80,000 capacity for the Colusseum, and

-- a search for "size of stadiums" shows that the Wikipedia page starts listing from 40,000 - up to 100,000 to 132,000 for just a dozen constructions, and

-- the Colosseum was built between 72 and 80 AD.

This must give an idea of the actual worth of the endeavour.