Short answers, pulled from the story.
Dante Alighieri wrote the Divine Comedy during his exile from Florence, which began in 1302 and lasted until his death. The political struggle between the White Guelphs and Black Guelphs in central Italy directly shaped the poem's themes and characters.
The Inferno consists of nine circles plus one entrance circle, totaling ten circles that descend through the underworld beneath Jerusalem. Each circle punishes specific sins through contrapasso, with the deepest circle reserved for Lucifer at the very bottom of the earth.
The Paradiso contains nine celestial spheres plus the Empyrean, totaling ten levels of heaven arranged concentrically. The seven lowest spheres deal with cardinal virtues while the eighth sphere holds the theological virtues and the ninth sphere contains angels.
The first printed edition of the Divine Comedy was published in Foligno, Italy, on the 11th of April 1472 by Johann Numeister and Evangelista Angelini da Trevi. Fourteen copies of the original 300 printed copies still survive today.
The poem discusses a spherical Earth with different stars visible in the Southern Hemisphere and altered sun positions. Dante also describes gravity changes when traveling through the Earth's center and uses Ptolemaic cosmology to structure the nine spheres of Heaven.