Four-pointed nails, already used in World War One, were thrown onto the city's main roads to sabotage the occupying forces and hinder their movements. They were made in large quantities by a Trastevere blacksmith, Enrico Ferola. Following a tip-off, on 19 March 1944 Ferola was arrested by the Koch gang, tortured and, on 24 March, executed at Fosse Ardeatine.