Thousands begin to gather in Vatican City for Pope Francis' inaugural Mass on Tuesday.

Up to one million people from around the world are expected to cram into St. Peter's Square and surrounding streets to join the celebration.

U.S. Vice President Joe Biden will be among the 130 religious and political delegations in attendance.

Among them will also be Ecumenical Patriarch Bartholomew from Istanbul.

It's the first time the spiritual head of Orthodox Christians will attend a Roman Catholic pope's inaugural Mass since the Great Schism between western and eastern Christianity in 1054.

Francis, the former Buenos Aires Cardinal Jorge Bergoglio, has aroused enormous enthusiasm and interest in the Catholic world.

(SOUNDBITE) (English) AMERICAN PILGRIM, MIKE, SAYING:

"It's a historical moment. I am excited to just be here, be a part of it."

(SOUNDBITE) (English) AMERICAN PILGRIM JERRY HORNE OF PRIESTS FOR LIFE, SAYING:

"We are very pleased