It depicts a key medieval event.
The coat of arms of the city of Avilés incorporated into the Water Font in front of the Church of San Francisco, an early source of potable water for the city. Photo by Sue Burke.
In 1248, a Castilian fleet sent by King Fernando III “the Saint” was attacking the city of Seville, at the time held by the Moors. But the way was blocked by an enormous chain that stretched between towers on either side of the Guadalquivir River; a chain like that was also used to protect the harbor of Constantinople. (One of Seville’s towers, known as the Gold Tower, still stands.)
A ship in the King’s fleet had been built and was crewed by men from Avilés, a city on the Atlantic Coast in northern Spain. A crew member had the idea to put large saw teeth on the prow of the ship, which then sailed up to the chain and, pushed up and down by the waves, slowly cut through it. Seville was taken, a key victory in the Reconquest of Spain.
Out of gratitude, King Fernando gave Avilés the right to recreate the event on its coat of arms: the ship, the saw, the chain, and the towers. That coat of arms is used by the city to this day.