The project was taken up by Paul II in 1471 and Sixtus IV in 1473, then shelved. One of the specialists involved was the Bolognese engineer and architect Aristotele Fioravanti. In about 1451, he had transported several large columns destined for the new choir of St. Peter's, and in 1455 he moved a bell-tower in Bologna probably using a screw mechanism, as implied in drawings dating from shortly after the event.
The traces of these projects are visible in the devices for moving obelisks, monolithic columns, and pyramids found in many fifteenth- and sixteenth-century manuscripts.
Moving the obelisk
The plan to move the Vatican obelisk was revived in the late sixteenth century. Sixtus V called for proposals in 1585, and the contract was won by Domenico Fontana.
The shifting of the monolith, which stood more than 90 feet tall and weighed nearly 661,200 lbs, was carried out in 1591 in three phases over a period of about five months. The work involved 900 people and 140 horses.
The obelisk, suspended by ropes from a giant wooden scaffolding, was eased onto a carriage rolling on cylinders. The carriage was then winched up to an earth embankment. In the final phase, the obelisk was placed upright again by means of the same scaffolding that had been used to recline it.