Martin P. Nilsson (1874-1967), Greek Piety
, tr. H.J. Rose (Oxford: Clarendon Press, 1948), p. 9:
We make a spot holy by putting a sanctuary there; but in antiquity, the holiness belonged to the place itself, and a sanctuary was erected there because the spot was holy. Zeus was surnamed after the mountains about whose summits he gathered his clouds, Artemis and other deities often after well-known sanctuaries. In addition, there were the countless swarms of godlings and semi-divine beings who often were worshipped only in a single spot. The Nymphs, who were much worshipped, particularly by women, had their cults in caves and beside springs. River-gods, whose popularity is made plain by the river-names which form part of personal names, as Kephisodotos, 'gift of the river Kephisos', had their places of worship at the river whose name the god bore. Purely topographical also was the penetration of human life by religion in ancient times, to a degree which we can hardly picture aright to ourselves. True, in modern Greece the little chapels in which, at most, Mass is said once a year are amazingly numerous; in some places every family has its chapel. But in ancient Greece the holy places were more numerous still. What Strabo says of the country at the mouth of the river Alpheios is true to some extent of all Greece.
All the region is full of shrines of Artemis, Aphrodite and the Nymphs, in groves full of flowers ... there are also many shrines of Hermes on the roads and of Poseidon on the sea-shore.
It was hardly possible to take a step outdoors without stumbling on a holy spot, a chapel, a sacred precinct, or at least a herm (pillar with a head of Hermes atop). An ancient writer said with but slight exaggeration that gods were more numerous than human beings.
Strabo 8.3.12 (tr. H.L. Jones):
The whole country is full of temples of Artemis, Aphroditê, and the Nymphs, being situated in sacred precincts that are generally full of flowers because of the abundance of water. And there are also numerous shrines of Hermes on the road-sides, and temples of Poseidon on the capes.
μεστὴ δ᾽ ἐστὶν ἡ γῆ πᾶσα ἀρτεμισίων τε καὶ ἀφροδισίων καὶ νυμφαίων ἐν ἄλσεσιν ἀνθέων πλέῳς τὸ πολὺ διὰ τὴν εὐυδρίαν, συχνὰ δὲ καὶ ἑρμεῖα ἐν ταῖς ὁδοῖς, ποσείδια δ᾽ ἐπὶ ταῖς ἀκταῖς.