n the first half of the seventeenth century the clash between France and Spain is re- flected in the north of the Italian peninsula: in the past allies, now enemies, the Duchy of Savoy and the State of Milan must necessarily strengthen the border that divides them. Sieges follow one another in a vain attempt by the French to come to Milan, and the Spaniards to drop Turin. The cities walls closest to the border are constantly monitored, estimated, enhanced. Military engineers at the service of the two countries are engaged to relief, project maintenance. Busca, Clarici, Lechuga, Baldovino, Prestino, Camassa, Beretta are alternated at the service of Milan’s governors, with others of the most pre- pared engineers of that time: they wonder constantly about changes, enhancements and adjustments to new strategic and defensive needs. The drawings, the «paper cities», now kept in European archives, tell us the many states, too many and ephemeral boundaries, the difficult defence of the many and never quiet borders.