Da Vinci illustrating the effects of the combination of two or more toothed wheels. Five wheels (four external). "Every wheel placed on one-half of the moving wheel ( the large central wheel) will turn in a direction opposite to those wheels moved by the other half." Madrid Ms. I (BNM) fol. 26v (detail). The Madrid Codices are two manuscripts by Leonardo da Vinci which were discovered in the Biblioteca Nacional de España in Madrid in 1964. Topics discussed include mechanics, statics, geometry and construction of fortifications. The manuscripts are of great importance as they contain about 15% of his notes referenced today, but are also important for the quality and relevance of the works they contain, which are among the major engineering treatises of their time. The Madrid Codices I was finished during 1490 and 1499, and II from 1503 to 1505.