The Jesuit church of Saint Ignazio was supposed to have a glorious dome, but when the money ran out in 1642, the plans were scrapped.
Instead of foregoing the dome entirely, painter and Jesuit brother Andrea Pozzo proposed that he paint a life-sized illusion of a dome that would fool the eyes of visitors (as long as they looked up from the proper angle).
His masterpiece still fools the eye today. Painted between 1685 and 1694, it is a remarkable piece of perspective work.
Pozzo painted another illusion for the barrel-vaunted ceiling of Saint Ignazio. The huge painting depicting the life and works of Saint Ignatius lifts and expands the simple building skyward, using forced perspectives to move figure up into the heights. The technique is known as quadratura, a mixture of geometrically accurate architecture in forced perspective and elements of fantasy, like cherubs and floating saints. Pozzo wrote a book on the subject called Perspectiva Pictorum and Architectorum, which was very influential with other Baroque painters.
Both the dome and the central illustration are painted on a single 17 meter canvas. His work on the illusions was so well received that he was granted the commission for the rest of the artwork in the church.
In April of 1891 an enormous powder magazine explosion just outside the city rocked Rome and damaged the ceiling artwork. (It also collapsed part of the roof of the Parliament building and sent the city into a general panic.) A restoration in 1961 repaired the illusion.
In 1703, Pozzo repeated his dome illusion in Vienna, in a Jesuit church now called the University Church, and at the Church of the Gesù in Frascati, Italy.
The best way to view the illusion is to enter the church, keeping your eyes low until you reach the circular marble marker that indicates the ideal vantage point for taking in the dome illusion. A second marker on the floor indicates the ideal viewing spot for the rest of the ceiling.