This is an outline of the universe as envisaged by educated people early in the 14th century, notably the Florentine poet Dante Alighieri (1265-1321), who described it in his master-work "The Divine Comedy". The result is a curious mixture of science, mostly derived from Aristotle and other ancient Greek writers, together with theological speculation.
Here is Dante, standing beside the Duomo in Florence.With his right hand he is indicating Hell, and behind him is Mount Purgatory, with Paradise in the heavens above.
The first point to be made is that it Dante knew that the world was round. Doubtless illiterate peasants thought it was flat, but all those familiar with the ancient writers knew otherwise. In Hellenistic times Eratosthenes had calculated the circumference of the earth, and had come up with a surprisingly accurate figure, but others had suggested it was smaller. There was even a notion of gravity: that all objects on the earth's surface were attracted towards its centre.
The old mediaeval maps had always shown Jerusalem at the centre of the earth's landmass, and indeed with the mapmakers' knowlege of the world being limited to Europe, western Asia and north Africa, with the whole being encircled by a single vast ocean, this did not involve too much distortion. But during Dante's lifetime Marco Polo returned from China, which he called "Cathay", and published an account of his travels a few years later; and for those who believed Polo (which not everyone did) it was apparent that Asia was considerably more extensive than was once thought. On the other hand, it is very unlikely that Viking stories from 300 years earlier, telling of voyages to lands beyond the north Atlantic, were known in Italy.
Speculative geographers of Dante's day thought it significant that all the known land was in the northern hemisphere of the earth, and they therefore suggested that to balance this there might be an undiscovered southern continent, "Terra Australis". Accordingly it was there that Dante placed Mount Purgatory, the highest peak in the world, directly opposite Jerusalem on the globe.
It was believed, following Aristotle and his successors, particularly Claudius Ptolemy (circa 90-168 A.D.), that the sun and all other heavenly bodies moved round the earth (this is known as the "Ptolemaic" system). It had been known for many centuries, if not thousands of years, that the stars moved in stately procession from east to west round the axis of the Pole Star ("clockwise" as it came to be called), with the constellations maintaining their shape and the time of their appearance in the heavens from year to year; but that there were certain bodies that looked like stars but behaved differently: sometimes not being seen for months at a time, or even longer, and sometimes moving backwards, from west to east (retrograde motion). These were named "planets", after the Greek word for "wanderers". Just five were visible to the naked eye, and they had been identified with the ancient Roman gods Mars, Mercury, Jupiter, Venus and Saturn. Together with the sun and the moon they gave the number seven; which as a prime number had occult significance and became identified with the days of the week (see footnote 1). The planets did not appear anywhere in the sky, however; they were only ever to be seen in a belt of constellations which also marked the path of the sun and moon across the heavens - the line of the zodiac. To the mediaeval mind, this could not be merely accidental, but must have some deep significance. But the great age of astrology came later, in the Renaissance, and will not be discussed here (see footnote 2)
Centuries of observation had shown that, of these heavenly bodies, the moon was closest to the earth, Venus and Mercury sometimes passed between the earth and the sun, and were therefore closer to us than the sun, whereas Jupiter and Saturn were beyond the sun, and the constellations of the "fixed stars" were further away still. (The only mistake made here by Dante and his contemporaries was to get the relative positions of Venus and Mercury wrong: they thought Mercury was closer to the earth and Venus closer to the sun). Aristotle had suggested that the planets were set in spheres of crystal too pure to be visible, and this belief persisted. So Dante's universe had the earth within a concentric system of transparent spheres in which were set, moving outwards, the Moon, Mercury, Venus, the Sun, Mars, Jupiter, Saturn, and finally the fixed stars. As to what made these spheres rotate around the earth, Aristotle could only suggest the following, and until the 17th century no-one had any better explanation. Beyond the fixed stars lay the "Primum Mobile", the "first mover", the "causeless cause" which initiated the motion of the heavenly bodies. And what lay beyond that? To Aristotle the question was meaningless: what could there be outside the universe? Outside it there was neither matter nor time. To Christians, however, the answer was clear: beyond the material universe was God.
It should not be imagined that people of Dante's day saw the universe as being small. Mediaeval writers believed that the sun was larger than the earth, and the fixed stars were larger still, and immensely distant: one estimate was that it would take 8,000 years of travelling to reach them! But the immensity of space was not seen as empty: on the contrary, it was filled with heavenly light; with angels, "intelligencies", blessed souls, all praising God.
The model would appear not only to place the earth at the centre of the universe, but Satan at the centre of the earth, and hence at the centre of all creation. But to a mediaeval mystic the opposite would be the case: the centre of the universe was God, and Satan was by comparison an infinitessimally tiny speck at the maximum possible distance from God.
In "The Divine Comedy" Dante first travels through Hell, guided by the ghost of the Roman poet Virgil. Hell is situated inside the earth, in the form of a gigantic funnel leading down through ever-lower circles of the damned, until they see at the very centre of the earth, Satan himself, "like a worm at the heart of an apple". The poets now pass the centre of the earth's gravity, and they discover Satan's legs are pointing now upwards. They climb through tunnels until they emerge at the foot of Mount Purgatory, on the directly opposite side of the earth from Jerusalem.
Mount Purgatory contains the souls of those sinners who have repented of their sins before death. They do not deserve eternal punishment, but must spend time being purged of their sins before being admitted to paradise, unlike the sinners in Hell, for whom there is no escape. (see footnote 3). The poets climb Mount Purgatory, evetually reaching the Earthly Paradise on the summit. From here Dante is carried up to Heaven: Virgil, being a pagan, can accompany him no further, and henceforth Dante will be guided by the ghost of his true love and muse, Beatrice. Aristotle had taught that the heavens are made of a different type of matter from earth, not subject to change and decay, and Dante's vision follows this. Dante and Beatrice journey through the spheres of heaven, meeting saints and angels, on through the Primum Mobile to what lies beyond, the Empyraeum. There Dante is granted a vision of God, not as a person, but as the Divine Light, the Love which is the motive force behind the universe. The poem ends.
For more information see C. S. Lewis: "The Discarded Image"
Footnote 1: Days of the week. In English the link between the heavenly bodies and the days of the week is obvious in Saturn-day, Sun-day and Moon-day, but the other days are named after the Saxon gods Tiw, Woden, Thor and Freya. These days are more obvious in French: Mardi, Mercredi, Jeudi and Vendredi, linking to Mars, Mercury, Jupiter and Venus. I remember seeing near Seville in Spain a Roman circular floor mosaic with the sun in the centre surrounded by the six gods and goddesses of the moon and the five visible planets. The fact that these heavenly bodies number seven was seen as having all sorts of mystical links: with the only seven metals known at the time (gold, silver, iron, mercury, tin, copper and lead), with the seven colours used in heraldry (gold, silver, red, black, blue, green and purple), with the seven deadly sins, and so forth. Thus Mars, the red planet, is linked with iron, with warfare, and with anger. This was more fruitful ground for Renaissance astrology.
Footnote 2: The zodiac: the 12 constellations forming the path through which the sun, the moon and the planets move. The constellations are not all of equal size, or equidistant from each other, or even in a straight line, but are treated by astrologers as having equal importance. The zodiac is most visible in midwinter, when the huge and easily identifiable constellation of Orion dominates the southern sky: above Orion and slightly to the right and left respectively are Taurus and Gemini. It is interesting that the astrological signs said to predominate at this time of the year: Saggitarius, Capricorn and Aquarius; cannot be seen at all in winter!
Footnote 3: Purgatory. Time in Purgatory was different from that on earth, and sinners might have to undergo thousands of earth-years of penance before they were fit for Paradise. In the middle ages the Pope could issue an Indulgence, which would remit time in Purgatory; for instance, to those going on a crusade. Remission could also be obtained by prayer or pilgrimage. Eventually it was believed that a simple cash payment could gain remission, either for the donor or for a deceased relative. This famously aroused the ire of Martin Luther, who denounced not only Indulgencies but the very notion of Purgatory, which he held was non-scriptural. In Luther's day, the Elector of Saxony, Frederick the Wise, possessed 19,000 holy relics, including a twig from the Crown of Thorns and another from Moses's Burning Bush, a crumb from the Last Supper, and 204 bits of the children massacred by Herod. Anyone who viewed these and made appropriate gifts of money would be excused two million years in Purgatory! It is easy to understand Luther's contempt!