Passage: To protect against frost, most of the aqueduct ran about 1 m below the Earth's surface. Archaeological excavations show that, at the lowest level, the Roman engineers had placed a loose layer of stones. On this base, they set a concrete or stone U-shaped groove for the water and, over this, cut stones and mortar were used to build a protective arch.

Question: how deep did the aqueduct run?
1 m