Pebble mosaics dating from the 4th century BC have been unearthed in Arta, Greece. During excavations at the Small Theatre of Ancient Amvrakia, the floor of a 12-foot wide bathhouse was revealed. Achaeologists discovered carefully laid mosaics of swans, octopuses, and winged cherubic figures  surrounded by a spiral border. Each design was formed using smooth river pebbles in white, off-white, and dark tones, with amber and red pebbles acting as accents. The dig was conducted by the Ephorate of Antiquities, in the town of Arta, which has been occupied on and off since ancient times.

Source: A Friendly Octopus Found Within Ancient River Pebble Mosaics in Greece