Ancient Greek literary sources claim that among the many deities worshipped by a typical Greek city-state (sing. polis, pl. poleis), one consistently held unique status as founding patron and protector of the polis, its citizens, governance and territories, as evidenced by the city's founding myth, and by high levels of investment in the deity's temple and civic cult. The temple of the deity involved was usually founded on the highest ground (acropolis) within the city walls, or elsewhere within the central public assembly space, the agora. Conversely, a city's possession of a patron deity was thought to be a mark of the city's status as polis.
Some poleis seem to have had several "patron gods" in sequence, or all at once. Some had more than one founder, or founding myth. A few would have superficially resembled a collection or tribal coalition of villages rather than the single, centralised entity suggested by the English term "city-state"; early Sparta provides a clear example of this. Some poleis seem to have had no distinct or identifiable patron deity.
Greek city-states
The rise of the polis seems to have coincided with Greek abandonment of kingship, and its replacement by warrior-aristocracies, and rulers elected by self-governing citizen communities. Greek city-states were governed from a prytaneion, a building thought to have functioned as a palace under monarchs, and otherwise as an administration centre, with a large reception hall that also housed the sacred "common hearth" of the polity.
Foundation deities
The hearth of every prytaneion and domestic household was sacred to the goddess Hestia, whose presence and cult within the prytaneion and households justified the civil, political and religious basis of the city's public life, and the community's decisions concerning treaties, laws, institutions and traditions. In founding a new colony, live embers of Hestia's fire were carried from the parent-polis to the colonial prytaneion, where they were used to kindle the new colony's sacred, sacrificial fire. Without an agora, sacrificial fire, altar and Hestia, there could be no city. This aside, poleis were largely self-defined; they need not be politically independent, they might use any of various regional Greek dialects and their size seems to have been an irrelevance to their definition as poleis, or modern identification as "city-states". Some were enclosed within larger states. Some had only 200-500 male citizens and no more than a few square kilometers of agricultural land. Others were very populous, or became so through confederation, with estimated populations of many thousands, and with lands and influence extending many miles into surrounding countryside, or across the Mediterranean Sea. Land hunger and warfare were endemic. The two largest and most powerful of these states, Sparta and Athens, mutually antagonistic for much of their history, both acknowledged the same protective deities. Where Sparta chose conquest and subjection of its Greek-speaking neighbours to the immediate west (see Mantinea), Athens used her navy to help establish new, colonial poleis much further afield.
Prospective founders of Greek city-states and colonies sought the approval and guidance not only of their "mother city" but of Apollo, through one or another of his various oracles. Apollo acted as consulting archegetes (founder) at Delphi, and among his various functions, he was patron god of colonies, architecture, constitutions and city planning. Greek colonies were founded throughout the Mediterranean world, some of them very distant from their "parent" cities. Based on epigraphic evidence Herman-Hansen (1994) estimate the number of Greek poleis to have been "over one thousand... including colonies", presuming a prytaneion a reliable indicator of a city-state, and thus, perhaps, of a patron deity. A legendary divine institution pertaining to "patron deities of the polis" seems evident in Apollodorus, Bibliotheca 3.14.1; "in the time of Kekrops, they say, the gods decided to take possession of cities in which each of them should receive his own peculiar worship". Plato's belief that every polis had a divine patron was carried into modern scholarship. "About 91" prytaneia are identified in literary sources. Prytaneia are archaeologically confirmed at Delos, Lato and Olympia, and six others are reasonably secure.