Sentence Completion

Complete the sentence with ONE word from the passage for each blank.

Venice was built on a cluster of low islands in a shallow lagoon, and its founders drove millions of wooden piles deep into the soft mud to support stone buildings. Cut off from oxygen underwater, the timber did not rot but instead hardened over centuries. Today, however, rising seas and sinking ground threaten the city, prompting the construction of mobile flood barriers to hold back high tides.

The buildings of Venice rest on wooden sunk into the mud, and the city is now protected from high tides by movable flood .