McDonald's has opened a franchise just steps away from the gleaming white marble dome of St. Peter's Basilica, giving indigestion to some cardinals and local business owners.

There was no fanfare for the Dec 30 opening of the US fast food giant's new venue behind a subdued exterior on the picturesque Borgo Pio, just outside the spiritual home of the world's 1.2 billion Roman Catholics.

When the plan emerged last year, one of its most strident critics was Cardinal Elio Sgreccia, who said McDonald's fare was far removed from Roman gastronomic traditions and not the healthiest of foods.

"The mega sandwich shop on Borgo Pio is a disgrace," Sgreccia told La Repubblica newspaper at the time.