ceive it originated from the circumstance, that the Duke had not long before established at Milan an academy for the study of painting, sculpture, and architecture, and was desirous that Leonardo should take the conduct and direction of it[1]. The second was, however, we find, the true motive; and we are further informed, that the invitation was accepted by Leonardo, that he went to Milan, and was already there in 1489 [2].
Among the collections of Leonardo still existing in manuscript, is a copy of a memorial presented by him to the Duke about 1490, of which Venturi has given an abridgment [3]. In it he offers to make for the Duke military bridges, which should be at the same time light and very solid, and to teach him the method of placing and defending them with security. When the object is to take any place, he can, he says, empty the ditch of its water; he knows, he adds, the art of constructing a subterraneous gallery under the ditches themselves, and of carrying it to the very spot that shall be wanted. If the fort is not built on a rock, he undertakes
