Very cool discovery in St Paul's

From the Telegraph:

Archaeologists digging to reach the tomb of St Paul have stumbled across a life-size "sketch" of the dome of St Peter's produced by one of its architects in the 16th century.
The excavation of St Paul's tomb at the church of St Paul's Outside-the-Walls in Rome is now complete, and the sarcophagus will be on view from the beginning of next year.
However, three feet below the floor of the enormous church, which is the second-largest in the city, the project's team came across a surprise from the Renaissance.
An architectural drawing of the arches and walls of the dome of St Peter's had been carved into 1,726 marble slabs by Giacomo Della Porta, who took over the design and construction work of the dome after the death of Michelangelo. The slabs had formed the floor of the church at the time.
"It was a complete surprise," said Carlo Visconti, one of the engineers. "It is a curious find, and perhaps we shall think about putting it on view to the pilgrims, tourists and students who will come to see St Paul's tomb."
He added that there was a simple explanation for the drawing. When Michelangelo died, he did not leave behind scale drawings of the dome. Consequently, Della Porta decided to sketch out the cupola in life-size and the only covered place large enough for him to work in was the church. "He needed to do the sketch to work out his calculations," said Giorgio Filippi, an architect at the Vatican.