The short answer is: earthquakes and popes, in that order.
For much more on the life and death of the Colosseum - and many other fascinating facts about the classical world - check out my book “Naked Statues, Fat Gladiators, and War Elephants: Frequently Asked Questions about the Ancient Greeks and Romans.”
https://www.amazon.com/Naked-Statues-Fat-Gladiators-Elephants/dp/1633887022
If you're interested in booking a tour of the Colosseum, I recommend Through Eternity Tours, a Rome-based company that specializes in custom, in-depth experiences. Save 5% on any private or group tour with the discount code TOLDINSTONE.
https://www.througheternity.com/en/colosseum-tours/
If you're so inclined, you can follow me elsewhere online:
https://www.patreon.com/toldinstone
https://www.reddit.com/r/AskHistorians/wiki/profiles/toldinstone
https://www.instagram.com/toldinstone/
https://www.goodreads.com/author/show/20993845.Garrett_Ryan
Chapters:
0:00 Introduction
0:30 Games of the Colosseum
1:43 Decline of the Games
3:15 The medieval Colosseum
5:37 The Colosseum during the Renaissance
Thanks for watching!