Soon after Leonardo’s arrival here—either because his reputation had preceded him or, more likely, because of Fra Luca Pacioli’s recommendations—he became directly involved with the defenses of Venice. Immediately he was sent on an inspection trip of the city’s existing defenses, especially those inland from where an invasion would probably come. When he had seen them, he recommended a system of defenses along the Isonzo river near the present border of Yugoslavia, using the river itself to the disadvantage of the enemy. He also made suggestions for the improvement of forts, and even drew up plans for a completely new type—a circular fort. This consisted of a central, circular fort surrounded by two belts of fortresses each separated by a moat. In the outside moat were four semicircular outposts. Communication was by underground galleries. The total absence of superstructure and projecting balconies was a new idea for the times. Another new defense idea was to station in the moat itself a low, thick tower almost completely submerged, defended by a thin opening near the waterline. It was reached from the main fort by an underground passage and the gunsmoke was removed by vents. According to Leonardo no enemy could conceal himself in any part of the defenses and not be seen from such an outpost. Leonardo’s most unusual scheme for defending Venice, however, was his idea of approaching an enemy fleet under the water and then putting holes in the hulls of their ships. Actually, the idea of diving was not a new one. Aristotle had written of diving and diving bells, and certainly the stories of pearl fishers in the Orient were well known in the Renaissance. But Leonardo designed a diver’s suit closely resembling those used today. This consisted of a complete suit of leather with helmet and eyepieces; it was made airtight by spirals of steel at the joints. He then added a bladder for holding air which fastened inside the suit at the diver’s chest. It is possible that Leonardo also invented an air chamber that could be used by the diver while under water—but he was very secretive about this invention for fear of how men might abuse such a discovery. He wrote, “... and this I do not publish or divulge, on account of the evil nature of man, who would practice assassinations at the bottom of the seas....”