A view of the complete mosaic that was found in the second reception hall, Exedra/tablinum, in the House of the Faun at Pompeii. This mosaic has almost one million tesserae. It measures 8 ft 11 in (2.72 m) x 16 ft 10 in (5.13 m). It depicts the battle between Alexander the Great and the Persia ruler, Darius III, in 333 BC at the site of Issus.
The mosaic, on the left side, shows Alexander who, astride his horse Bucephalus, leads his men against the fleeing Persians. Opposite Alexander towers the figure of Darius on his retreating war chariot. Between the two is a Persian prince who displays his loyalty by using his body to shield his king, while a soldier offers him his own horse, thus condemning himself to certain death.
The use of opus vermiculatum (a technique of mosaic which uses very small tesserae) enabled the craftsman to render all the effects of luminosity, the changes in colour, the details of the armour and the faces, and even the moods.
Most scholarship agrees that the mosaic is a copy of an original Greek painting.
Sources of information: Museo Archeologico Nazionale di Napoli and Wikipeida