Short answers, pulled from the story.
Workers in Mesopotamia laid colored stones and shells into plaster to create patterns at a temple building in Abra during the second half of the 3rd millennium BC. These earliest known examples used pieces of ivory alongside natural pebbles to reinforce floors rather than decorate them.
Two main methods emerged: opus vermiculatum used tiny cubes of stone or glass measuring 4 millimeters or less to achieve fine detail, while opus tessellatum employed larger pieces laid directly on site. Roman architects later adopted these techniques to cover walls and ceilings in structures like the Domus Aurea built by Nero in 64 AD.
Emperor Justinian commissioned great buildings like the Hagia Sophia in Constantinople and the Nea Church in Jerusalem from the 6th to the 15th centuries. Surviving fragments from the Great Palace of Constantinople include a portrait of a moustached man likely identified as a Gothic chieftain, considered the most important surviving mosaic of the Justinianian age.
William II of Sicily ordered the Monreale Cathedral built between 1176 and 1186 covering 0.75 hectares with at least 100 million glass and stone tesserae. This massive project included narrative scenes similar to those found in the Cappella Palatina but replaced royal portraits with biblical stories.
The Madaba Map created between 542 and 570 serves as the single most important piece of Byzantine Christian mosaic art in the East depicting an area from Lebanon to the Nile Delta. This cartographic masterpiece was rediscovered in 1894 and remains the oldest surviving map of the Holy Land with detailed naturalistic features like animals and fishing boats.