A phylarch is a Greek title meaning "ruler of a tribe", from phyle

Phyle

Phyle is an ancient Greek term for clan or tribe. They were usually ruled by a basileus...

, "tribe" + archein "to rule".

In Classical Athens

Classical Athens

The city of Athens during the classical period of Ancient Greece was a notable polis of Attica, Greece, leading the Delian League in the Peloponnesian War against Sparta and the Peloponnesian League. Athenian democracy was established in 508 BC under Cleisthenes following the tyranny of Hippias...

, a phylarch was the elected commander of the cavalry provided by each of the city's ten tribes.

In the later Roman Empire of the 4th to 7th centuries, the title was given to the leading princes of the Empire's Arab

Arab

Arab people, also known as Arabs , are a panethnicity primarily living in the Arab world, which is located in Western Asia and North Africa. They are identified as such on one or more of genealogical, linguistic, or cultural grounds, with tribal affiliations, and intra-tribal relationships playing...

 allies in the East (essentially the equivalent to "sheikh

Sheikh

Not to be confused with sikhSheikh — also spelled Sheik or Shaikh, or transliterated as Shaykh — is an honorific in the Arabic language that literally means "elder" and carries the meaning "leader and/or governor"...

"), both those settled within the Empire and outside. From ca. 530 to ca. 585, the individual phylarchs were subordinated to a supreme phylarch from the Ghassanid dynasty.