Dante Alighieri opens Canto IV of The Inferno with the scene of Dante the Pilgrim and his guide Virgil preparing to descend into the first circle of Hell, recounting his sorrow upon gazing down unto Limbo:

“True it is, that upon the verge I found me
Of the abysmal valley dolorous,
That gathers thunder of infinite ululations.
Obscure, profound it was, and nebulous,
So that by fixing on its depths my sight
Nothing whatever I discerned therein.”

And they continue downward, describing Limbo’s inhabitants:

Virgil: “Let us descend now into the blind world…
… I will be first, and thou shalt second be”

Dante: Thus he went in, and thus he made me enter
The foremost circle that surrounds the abyss.
There, in so far as I had power to hear
Were lamentations none, but only sighs…
And this arose from sorrow, without torment,
Of infants and of women and of men.

Virgil: “[These spirits] sinned not, and if they merit had,
‘Tis not enough, because they had not baptism
…
And if they were before [the time of] Christianity,
In the right manner they adored not God;
For such defects and not for other guilt,
Lost are they, and are only so far punished,
That without hope they live on in desire.

Unlike Hell proper, Limbo does not harbor sinners – it is the outermost region of Hell where the unbaptized reside. Because they lack sin, they do not suffer physical punishment. The extent of their suffering is the mental anguish resulting from their hopeless longing for the understanding of God.

According to Church doctrine, only infants who were not baptized (i.e. those that died shortly after birth) inhabited Limbo after Christ harrowed Hell, when, after his death and before his resurrection, he took the Hebrew patriarchs and matriarchs out of Hell and up to Paradise with him [1]. Dante goes against this precedent, including in Limbo the virtuous pagans who lived before Christ. Among them are Homer, Socrates, Plato, Seneca, Euclid, Ptolemy, and many others of similar caliber. Placing them in Limbo instead of Hell, Dante exalts the virtuous pagans, describing them as “honorable”, “mighty”, and “sovereign”; and Virgil (who is also of this group) leads Dante through Hell, providing him with the hope of salvation which he himself can not attain.

It is clear Dante held the virtuous pagans in high regard. Why then, had he placed them in Limbo and not Heaven? Intuitively, one might think he had done this to appease the demands of Church doctrine. Yet, from the wider perspective of how medieval theologians deal with virtuous pagans and their fate after death, it appears this is not the case [2]. There were various approaches that Dante could have used to “bend the rules” and permit his virtuous pagans into Heaven (see [2] for more details). However, Dante purposely excludes them from Heaven.

Marenbon [2] argues that Dante’s positioning of the virtuous pagans in Limbo can be explained on the hypothesis that Dante was strongly influenced by a medieval school of philosophy known as Averroism (a form of Scholasticism). The Averroists believe that humans have two different ends, earthly happiness and heavenly happiness, and that we must reach these two kinds of happiness through different means. We come to the first through the teachings of philosophy; whereas we attain the second through spiritual teachings which transcend human reason. The means and the ends to attain them have been shown to us on the one hand by human reason and on the other hand by the holy spirit.

The key notion of Dante’s take on Averroism is the distinction between the ends attained by way of reason and of spirituality – Although these ends are both described as “happiness”, they are not one and the same. Exercising one’s ability to reason, however virtuous, is not a sufficient means to the end of exalting one’s spirituality and finding meaning in life. In Purgatorio Canto III, Dante elaborates on this separation and its relation to hopeless desire and the fate of the virtuous pagan [2]:

Anyone is a fool who hopes that our reason
Can traverse the infinite path
Taken by one substance in three persons.
Remain content, human race,
With the fact that it is so [as opposed to why it is],
For, had you been able to see everything,
There would have been no need
For Mary to have given birth;
And you have seen those desire fruitlessly
Who would [had it been possible] have fulfuilled their desire,
Which is given to them eternally as punishment:
I mean Aristotle and Plato and many others…

It is interesting that while Dante affirms the distinction of these two ends, in their pursuit of knowledge the pagans are in some sense further from God than are the infants, who, ignorant of the reasons for their suffering, know not of the existence of the beatific vision of which they are deprived. This is to suggest the pursuit of earthly happiness in absence of harmony with the spiritual is at best a futile attempt to reach an end, and at worst amplifies the dichotomy of reason and spirituality, delivering man further from the enlightenment he yearns for.

Sources and further reading:
[1] Henry Wadsworth Longfellow, in his translation of Dante’s Inferno
[2] John Marenbon, Vertical Readings in Dante’s Comedy, Volume I Ch 1.ii.4
[3] Averroism
[4] Scholasticism