Il Convivio (The Banquet) is an unfinished book Dante wrote from about 1304–07. Its title refers to the banquet of human knowledge contained within, which he intended as an encyclopedia similar to those written by his dear mentor Brunetto Latini, Li Livres dou Trésor and Tesoretto. The first part serves as a general intro, and the next three parts each have a long poem followed by a commentary or allegorical interpretation serving as a jumping-board for many different subjects—astronomy, politics, linguistics, history, science, mathematics, nobility, virtues, philosophy, theology, love.
Unless we miraculously discover Dante’s original notes for The Divine Comedy with dates, and/or a secondary paper trail such as letters or journal entries, we’ll probably never know when exactly he began composing his magnum opus. However, some scholars believe he may have been working on it as early as 1304, or even started it before his exile and resumed writing after a Good Samaritan reunited him with those precious pages.
Thus, he may have at one point been writing Il Convivio and La Commedia simultaneously.
Obviously, Dante ultimately abandoned Il Convivio to focus solely upon his magnum opus. Yet this unfinished book wasn’t written in vain, since many of the ideas expressed therein found their way into the Commedia. Not only that, the Commedia is in many ways an extension of Il Convivio. If it were just an ordinary epic poem about the afterlife and Dante’s spiritual reformation, it wouldn’t be peppered with so many historical figures, astronomical calculations, geographical references, or philosophical and theological points!
Dante’s great-great-grandfather Cacciaguida degli Elisei, the poem’s fifth-most recurring character after Statius, appears from Cantos XV–XVIII of Paradiso and merits 550 lines. During his lengthy addresses to his descendant, he entreats Dante to be brave and reveal the whole truth, however unflattering, about well-known people. By only including people of renown, he’ll ensure lasting fame and power for himself and his poem.
Think about it. Would the poem have had the same impact if everyone Dante met were Guido and Gianna Nobody down the street, or purely fictional characters? It was easier for his audience to grasp all these deeper lessons precisely because he used real people everyone knew, both contemporaries and important historical figures. Besides, Dante always presents this as a real story, and many people absolutely believed him. (I’m inclined to believe he may have experienced at least some of these things in dreams or intense visions.)
Sure, these aren’t household names to most modern people, unless they’re Medieval history scholars, but Dante’s original audience didn’t need any footnotes to know who they were or the details about their lives.
Additionally, his original audience was Italian. Of course he primarily used people from their native land and Classical Antiquity. It wouldn’t have had the same impact if the poem were peopled with Germans, Russians, Englishmen, Chinese, Turks, or Egyptians. In an era long before instant mass communications and easily-available translations, people knew more about their own backyards than the wider world.
Dante did intend his poem first and foremost as a religious instruction manual to help other people who lost the way just as he did. But many of the components don’t relate to theology at all. They’re in there to finish the encyclopedic job Il Convivio started and celebrate the banquet of all existing human knowledge.