Justinian was able to go from the fires of the Nika Riots to opening his massive church in five years. I know the Romans/Byzantines had massive resources at their disposal (and some corners we're probably cut since the dome did fall a few decades later) but still how was it built so fast compared to Notre Dame?

Was it simply the amount of resources a continental empire could bring to the table compared to relatively small European towns? Even still five years vs two hundred years is an insane difference.