The cathedral closed at 2:30 a.m. (12:00 a.m. GMT) on Friday and re-opened at 5:40 a.m. (3:40 a.m. GMT), TASS reported.
The funeral will be held on April 26. Heads of state and government, royals, and representatives of various churches will arrive to attend the ceremony.
Unprecedented security measures involving roughly 11,000 police officers and troops are in place in Rome.
MNA