The following ranks W21–1 along with N75–136 and S1–61 are all of horsemen and constitute 46% of the whole frieze. They are divided into two lines of ten ranks – the same number as that of the Attic tribes. All figures are beardless youths with the exception of two, W8 and W15, who along with S2–7 wear Thracian dress of fur cap, a patterned cloak, and high boots; these have been identified by Martin Robertson as "hipparchs". Next are the four-horse chariots, each with charioteer and armed passenger, there are ten on the south frieze and eleven on the north. Since these passengers are sometimes depicted as dismounting they may be taken to represent the "apobatai", participants in the ceremonial race found in Attica and Boeotia.