The style of mosaic used to recreate this historic battle of Alexander the Great defeating the Persians in 333 BC, is called "opus vermiculatum" or "in the style of worms". It was made using tiny (under 4 mm) cut pieces of colored stones and glass, called 'tesserae', set in worm-like rows and placed into the floor. The Alexander mosaic used approximately 4 million tesserae.
Other mosaics that were in the House of the Faun and can now be found at the Archaeological Museum of Naples include the Cat and Hen Mosaic, the Dove Mosaic, and the Tiger Rider Mosaic.
Sources
For more on the archaeology of Pompeii, see Pompeii: Buried in Ashes.
Beard, Mary. 2008. The Fires of Vesuvius: Pompeii Lost and Found. Harvard University Press, Cambridge.
Christensen, Alexis. 2006. From palaces to Pompeii: The architectural and social context of Hellenistic floor mosaics in the House of the Faun. PhD dissertation, Department of Classics, Florida State University.
Mau, August. 1902. Pompeii, Its Life and Art. Translated by Francis Wiley Kelsey. The MacMillan Company.
