must be 300 braccia, each street receiving its light through the
openings of the upper streets, and at each arch must be a winding
stair on a circular plan because the corners of square ones are
always fouled; they must be wide, and at the first vault there must
be a door entering into public privies and the said stairs lead from
the upper to the lower streets and the high level streets begin
outside the city gates and slope up till at these gates they have
attained the height of 6 braccia. Let such a city be built near the
sea or a large river in order that the dirt of the city may be
carried off by the water.