Did they really build sets that big in those days?
The chariot race scene alone was tremendous, even for today.
shareWell, yes and no.
The lower half of that set was indeed constructed full-size, but the upper levels employed what were called "hanging miniatures."
It's difficult to describe without visual aids, but the way they worked was that a reduced-scale model of what would have been the upper half of the set was suspended by wires close to the camera, between it and the full-size set, with everything lined up perfectly for the lens so that they matched seamlessly on film.
When shooting exteriors, one advantage this method had over "glass shots," another common device of the day (wherein the camera was aimed through a pane of glass, onto which un-constructed portions of the set - including appropriate shadows - had been painted), was that the sunlight falling onto the miniature would always match that illuminating the full-size set.
I hope I explained all that in a way that made sense.
Poe! You are...avenged!