Mosaic, the art of arranging small pieces of material to create a larger image, is one of the oldest and most durable artistic techniques, having its start as wall decoration in ancient Mesopotamia. By 200 BCE, the invention of tiny square tiles called “tesserae” allowed Greek artisans to create highly detailed mosaics that rivaled the clarity of painting. During the Byzantine era, mosaic became the leading pictorial art for cathedrals and mosques alike. At the Hagia Sophia in Istanbul and the Cordoba Mosque in Spain, artisans adhered thousands of gold-leaf tiles to domed ceilings, transforming them into shimmering spaces symbolic of the heavenly realm. While mosaic was reserved for religious spaces for much of its history, modern and contemporary artists like Antoni Gaudí and Niki de Saint Phalle have brought this medium to public spaces by adorning parks and city walls with playful ceramic tiles.