In the Acropolis Museum Block III and the plaster cast of its relief decoration are exhibited separately. The relief surface now kept in the British Museum was forcibly removed with the use of crowbars by the men working for Thomas Bruce, lord of Elgin.

Block III depicts two horsemen galloping to the viewer’s right. The leading rider, tightly wrapped in his chlamys, is barefoot. Between his horse’s forelegs is discerned the tail of the preceding horse shown on the previous Block IV (Ακρ. 20033). The second rider leans backwards pulling his horse’s rein. His chlamys is fastened on his right shoulder and falls over his left forearm leaving his torso naked.

The frieze on the south side of the Parthenon depicts part of the procession formed by the people of Athens during the Panathenaic festival in honour of the protectress of the city, Athena. The procession's destination was the Temple of Athena Polias on the Acropolis. Its purpose was the transportation of the Panathenaic peplos destined to adorn the age-old xoanon of the goddess and the offer of a grand sacrifice of animals at the Great Altar outside of the temple.

On the south frieze the procession moves along the Panathenaic Way. Youths that lead sacrificial young cows precede. They are followed by more young men who carry offerings. Behind them come musicians with guitars, officials holding olive branches, eleven chariots that participate in an equestrian event, and finally sixty riders divided in ten groups.

The south frieze is fragmentarily preserved due to the bombardment of the Parthenon by the Venetians under the command of general Francesco Morosini in 1687 which caused extensive damages to the middle of the long sides of the temple. The drawings attributed to the painter Jacques Carrey, who visited the Acropolis in 1674, just thirteen years before its bombardment by Morosini, are an invaluable resource for our understanding of quite a few parts of this side of the frieze (Blocks XX - XXXVIII). Three blocks (XXII, XXX και XXXVIII) were already lost by then as they were removed during the conversion of the Parthenon into a Christian church so that windows would be opened in the blocks' positions.

The initial length of the south frieze was 58.70 m and consisted of 47 blocks. Today the blocks are divided between the Acropolis Museum and the British Museum in London, where they ended up after they were removed by Thomas Bruce, the lord of Elgin, in 1801-1804 when Greece was still under Ottoman occupation. In order to facilitate their transportation, Elgin's workmen, cut off with saws or crowbars only the faces of the blocks that bore the relief decoration. The Acropolis Museum exhibition includes the plaster casts of these blocks' faces on which some of the original fragments that fell off the monument, and thus escaped the looting, have been adjusted.