Nonetheless, the composition and general disposition of the figures, in which all lines and attention intersect at the mural's center—the head of Christ outlined against a clear sky and landscape—reveal a power of invention and a sublimity of spiritual content that mark the painting among the world's masterpieces.
His engagement took him to central Italy to study swamp reclamation projects in Piombino and to tour the cities of Romagna.
At Urbino he met Niccolò Machiavelli, who later became a close friend.
In 1978 a major (and controversial) restoration was begun, and in 1994–95 protective air-filtration and climate-control equipment were installed.
The restoration was completed in 1999, leaving the mural brightened considerably with some details clarified, but also revealing the extensive loss of the original painting.
In 1490 he was employed with Francesco di Giorgio as consulting engineer on the restoration of the cathedral at Pavia and later on the cathedral at Piacenza.
In 1483, Leonardo, with his pupil Ambrogio de Predis, was commissioned to execute the famous he did not use traditional fresco technique—account in part for its disintegration, which was already noticed by 1517, and subsequent deterioration and repeated restorations obliterated details and individual figures.
Many drawings of plans and elevations for domed churches reflect a concern with architectural problems that must have been stimulated by contact with Bramante during these years.
He worked c.1488 on a model for the tambour and dome of the cathedral at Milan.
Early in his apprenticeship he painted an angel, and perhaps portions of the landscape, in Verrocchio's (Uffizi) commissioned in 1481 by the monks of San Donato a Scopeto.
In this work is revealed the integration of dramatic movement and chiaroscuro that characterizes the master's mature style.