According to the inscription, this sheet records ideas for the drum of the cathedral of Monza, where Carlone worked on one of his most important commissions in Northern Italy. Frescoed with the aid of his assistants and quadraturisti Eugenio Ricci and Giacomo Lecchi between 1738 and 1744, the church’s decoration is partly inspired by its greatest treasure: the Corona ferrea, an early medieval crown thought to have been made of an iron nail of the True Cross. At the top of the Landolt drawing Constantine’s vision of the Cross is depcited, and at the bottom a seated female saint, likely to be identified with Saint Helen. For drawings by Carlone, see G. Biavati, ‘Tre disegni inediti di Carlo Innocenzo Carloni: proposta per un’indagine sulla sua attività di disegnatore’, Arte lombarda, new series, XLIX, 1978, pp. 60-67.