The Roman engineers had to adjust to local conditions all the time. See: Pompeii. Pompeii roads aren't like normal Roman roads. Because digging down was so d

The Roman engineers had to adjust to local conditions all the time. See: Pompeii. Pompeii roads aren't like normal Roman roads. Because digging down was so difficult in Pompeii, they chose to add material to grade the roads for drainage rather than dig them out.