He first made a small-scale sketch of the composition, sometimes including a large variety of figures.

Then he went to the living models, and studied portions of the whole design in careful transcripts from Nature, using black and red chalk, pen, and sometimes bistre.

Among the most admirable of his drawings left to us are several which were clearly executed with a view to one or other of these great Cartoons.

Finally, returning to the first composition, he repeated that, or so much of it as could be transferred to a single sheet, on the exact scale of the intended fresco.

These enlarged drawings were applied to the wet surface of the plaster, and their outlines pricked in with dots to guide the painter in his brush-work.
When we reflect upon the extent of the Sistine vault (it is estimated at more than 10,000 square feet of surface), and the difficulties presented by its curves, lunettes, spandrels, and pendentives; when we remember that this enormous space is alive with 343 figures in every conceivable attitude, some of them twelve feet in height, those seated as prophets and sibyls measuring nearly eighteen feet when upright, all animated with extraordinary vigour, presenting types of the utmost variety and vivid beauty, imagination quails before the intellectual energy which could first conceive a scheme so complex, and then carry it out with mathematical precision in its minutest details.
The date on which Michelangelo actually began to paint the fresco is not certain.