Such was the trenchancy and temper of his weapons that much of what he advanced has stood the test of time.
[Sidenote: The Donation of Constantine] The papal claim to temporal supremacy in the Western world rested largely on a spurious document known as the Donation of Constantine.
In this the emperor is represented as withdrawing from Rome in order to leave it to the pope, to whom, in return for being cured of leprosy, he gives the whole Occident.

An uncritical age had received this forgery for five or six centuries without question.

Doubt had been cast on it by Nicholas of Cusa and Reginald Peacock, but Valla demolished it.

He showed that no historian had spoken of it; that there was no time at which it could have occurred; that it is contradicted by other contemporary acts; that the barbarous style contains {49} expressions of Greek, Hebrew, and German origin; that the testimony of numismatics is against it; and that the author knew nothing of the antiquities of Rome, into whose council he introduced satraps.

Valla's work was so thoroughly done that the document, embodied as were its conclusions in the Canon Law, has never found a reputable defender since.