Around the inside of the dome is written, in letters 2 metres (6.6 ft) high:
TV ES PETRVS ET SVPER HANC PETRAM AEDIFICABO ECCLESIAM MEAM. TIBI DABO CLAVES REGNI
CAELORVM
(You are Peter, and on this rock I will build my church. I will give you the keys
of the kingdom of heaven.
Vulgate, Matthew 16:18–19.)