While this expedition was going on he proposed to dig a canal through the isthmus of Corinth, and had already put Anienus in charge of this undertaking. He also planned to divert the Tiber just below the city into a deep channel, which would bend round towards Circeii and come out into the sea at Terracina, so that there would be a safe and easy passage for merchantmen to Rome. Then too he proposed to drain the marshes by Pometia and Setia and to create a plain which could be cultivated by many thousands of men. He also intended to build great breakwaters along the coast where the sea is nearest to Rome, to clear away all the obstructions which were a danger to shipping at Ostia, and to construct harbors and roadsteads big enough for the great fleets which would lie at anchor there.