Loot:
3 Shards of wood from the Round Table.
One Rusted Helmet from The Trojan War
Jack The ripper's Knives 1 complete set
Defenses:
All Artifacts are under 24 hours electronic surveillance. Each artifact has a electronic camera dedicated to the, and each is in a case that detects when it's broken and when the heat is increased within the case.
If one of those detects something strange going on two guards will be sent to investigate. If these guards find anything strange or, don't report back then eight more guards will be on the spot.
Finally The museum is right over the largest school of arcane knowledge in the world. If it's determined that a magic is in use to steal the artifacts then a single mage will appear to try to stop you.