Oswald Spengler, answered from the texts and cited to the page.
The prime symbol is not a concept one arrives at by definition — it is something felt before it is named, and the feeling is the point. Every high Culture, at the moment of its awakening, seizes upon one fundamental form of the extended world and makes that form the ground of everything it subsequently builds, thinks, worships, and governs.
This seizure happens in the soul before it happens in philosophy; it is simultaneous with what I call the birth of the outer world, the child's first genuine grasp of depth and distance as something that speaks to the soul rather than merely pressing upon the senses.1 The prime symbol is that original form, unfolding in the young soul of a Culture as inevitably as the emerging butterfly unfolds its wings.2
For the Classical or Apollonian soul, the prime symbol is the bounded, sensuously present body — the near, strictly limited, self-contained thing that can be seen and touched.3 Everything Apollonian flows from this: the nude statue, mechanical statics, the city-state as a political body that does not reach beyond what the eye can survey, the phallus-symbol, the Olympian gods as individual presences with distinct and visible form.4
For the Faustian soul — the soul of the West — the prime symbol is pure and limitless space, the infinitely wide and infinitely profound three-dimensional extension into which the will drives without rest.5 Hence the art of the fugue, Galilean dynamics, the great Baroque dynasties with their cabinet diplomacy spanning continents, the destiny of Lear, the Madonna-ideal as an infinite longing rather than a sensuous presence.6
And the Magian soul, born in the lands between the Nile and the Tigris in the time of Augustus, takes the world-as-cavern as its prime symbol — a domed enclosure of light contending against darkness, neither the Classical body nor the Faustian infinite, but a traversed and swaying space in which light and dark are themselves substances, powers that have entity and contend.7
The prime symbol is not chosen. It is not the result of philosophical deliberation. It is innate insofar as it is an original possession of the soul of a Culture, and acquired insofar as every individual soul re-enacts that creative act for itself in early childhood.8 The same symbol governs the highest mystical experience of each Culture: whether Giordano Bruno feels himself a vanishingly small point in a star-filled infinity, or Jesus and his companions inhabit a world set under a domed light-cavern, or the Orphics take a bodily god into themselves — the deep urge of the soul is governed always by the prime symbol of the particular Culture and of no other.9
Mathematics, religion, politics, art, the very form of the state: all are expressions of this one original act of world-perception, ramifying across centuries.
with the soul's awakening, direction, too, first reaches living expression... the birth of its outer world through the symbol of extension; and thenceforth this symbol is and remains the prime symbol of that life, imparting to it its specific style and the historical form in which it progressively actualizes its inward possibilities.The Decline of the West Vol I, Form and Actuality, pp. 205–206
every individual soul re-enacts for itself that creative act and unfolds in early childhood the symbol of depth to which its existence is predestined, as the emerging butterfly unfolds its wings.The Decline of the West Vol I, Form and Actuality, pp. 205–206
for the Classical world-view the near, strictly limited, self-contained BodyThe Decline of the West Vol I, Form and Actuality, pp. 205–206
Apollonian are: mechanical statics, the sensuous cult of the Olympian gods, the politically individual city-states of Greece, the doom of OEdipus and the phallus-symbol.The Decline of the West Vol I, Form and Actuality, pp. 214–215
for the Western infinitely wide and infinitely profound three-dimensional SpaceThe Decline of the West Vol I, Form and Actuality, pp. 205–206
Faustian are: Galileian dynamics, Catholic and Protestant dogmatics, the great dynasties of the Baroque with their cabinet diplomacy, the destiny of Lear and the Madonna-ideal from Dante's Beatrice to the last line of Faust II.The Decline of the West Vol I, Form and Actuality, pp. 214–215
The world, as spread out for the Magian waking-consciousness, possesses a kind of extension that may be called cavern-like... The light shines through the cavern and battles against the darkness (John i, 5). Both are Magian substances.The Decline of the West Vol II, Perspectives of World-History, pp. 244–246
this prime form of the world is innate insofar as it is an original possession of the soul of that Culture which is expressed by our life as a whole, and acquired insofar that every individual soul re-enacts for itself that creative act.The Decline of the West Vol I, Form and Actuality, pp. 205–206
the deep urge of the soul is governed always by the prime symbol of the particular Culture and of no other.The Decline of the West Vol II, Perspectives of World-History, p. 292