By Steve Tawa

PHILADELPHIA (CBS) — The Greek Orthodox Archdiocese of America is holding its Congress in Philadelphia, during which high-ranking clergy and lay people are discussing the Orthodox-Christian family.

Mayor Nutter welcomed the Congress to Philadelphia, including Archbishop Demetrios, who leads the Greek Church in America.

If any of the attendees care to break away from workshops to see the city, the Mayor will put in a good word:

“If you come to my office, I will write you an excuse note. I’m not sure what it’ll get you,” Nutter joked.

Also in attendance are the Metropolitans who lead about 550 parishes across the United States, the equivalent of dioceses, based in New Jersey, Boston, Chicago, San Francisco, Pittsburgh, Atlanta, Detroit and Denver.

In a first for the Congress, Ecumenical Patriarch Bartholomew spoke to the gathering via Skype from Istanbul, Turkey.

Bartholomew is the spiritual leader of the Orthodox Christians around the world.

Vice President Biden is set to address the group at its grand banquet Wednesday evening.