Virgil explains that, like himself, the people damned to spend eternity in Limbo were not baptized—they either lived before the Gospel or died before their baptisms could take place. None of the people in Limbo are particularly evil; however, they did not achieve the redemption required to enter heaven.

Virgil refers to Christ's Harrowing of Hell, an episode following Christ's crucifixion when he descended into Hell and "rescued" several biblical figures, including Adam, Abel, Noah, Abraham, Jacob and his twelve sons, Isaac, and Rachel.

In traditional Roman Catholic doctrine, an infant who is not baptized and who dies, cannot go the Heaven because he or she is still considered to bear original sin. Baptism is the minimum means of entrance into Heaven (Paradiso).

When Dante awakes from his fainting spell, he and Virgil are in the First Circle of Inferno, known as Limbo, where worthy pagans and infants who died before being baptized are kept.

Lucretia, wife of Tarquinius Collatinus, was raped by Sextus, son of Lucius Tarquinius Superbus. After revealing this shame, she committed suicide.

In other words, Dante is honored just to be in their company, to the extent that his own sense of self-worth rises due to the illustriousness of his context.

The first group Virgil and Dante encounter in the castle-girded meadow encompasses important civil and military figures from Trojan and Roman history.

The seven gates of the castle allude to the seven moral virtues of traditional Christian doctrine: chastity, temperance, charity, diligence, patience, kindness, and humility.

The seven walls of the castle are often read as an allusion to the seven liberal arts: grammar, logic, rhetoric, geometry, astronomy, arithmetic, and music.

Limbo, although not an unpleasant place, is a kind of neutral zone in which no one is punished or rewarded.  From Virgil's perspective, its inhabitants are lost because they have no place to live other than this "holding tank."

Virgil and Dante are in Limbo, and Virgil pities the inhabitants because they are pagans and pre-Christian people who led nobles lives as well as the souls of unbaptized infants. Virgil himself is in this category.

Avicen—often known as Avicenna—was an Arabic philosopher and author of a medical textbook. Averroes was a Spanish Islamic philosopher who wrote a well-known commentary on Aristotle. Scholars have argued that Dante's inclusion of these Islamists (as well as Saladin) is evidence of Dante's hostility towards Islam. There are mosques in the Dis (Canto 8) and Mohammad is found among the damned (Canto 28).  

Euclid was a Greek geometer who wrote the Elements of Geometry in the third century BCE. Ptolemy was an Egyptian astronomer who in the second century CE devised the geocentric model of the universe which prevailed until the scientific revolution of the 16th century. 

By placing the mythical figures Orpheus and Linus together with the historical figures Tully and Seneca, Dante seems to be suggesting that poetry and values, as well as fiction and fact, exist side-by-side. 

Both Hippocrates (for whom the "Hippocratic Oath is named) and Galenus were Greek physicians. 

Pedanius Dioscorides was a first-century Greek scienitist and physician. He was the author of De materia media, a volume that cataloged the uses of medicinal plants. 

Aristotle (384–322 BCE) is the unnamed "master of the sapient throng" to whom Dante refers. When Aristotle's works were translated into Latin, they were disseminated through Christendom through the efforts of the Italian friar and philosopher Saint Thomas Aquinas (1225–1275 CE). The other philosophers mentioned here are known as the pre-Socratic philosophers, the Greek thinkers who preceded Socrates (470–399 BCE) and Plato (428–348 BCE)—the two primary founders of the Western philosophical tradition.

Marcia was married to Cato the Younger, the Roman statesman. Julia was Caesar's daughter and Pompey's wife. Cornelia was the daughter of Scipio Africanus and the mother of the tribunes, Caius and Tiberius, together known as the "Gracchi." 

Lucius Tarquinius Superbus was the last of the great Roman kings. Superbus's son, Sextus Tarquinius, raped Lucretia, an event which led to the king's banishment, ordered by Lucius Junius Brutus. Brutus was the brother of Lucretia and the nephew of Tarquin. Note: this is not the same Brutus as Julius Caesar's assassin, Marcus Junius Brutus. 

Soldan—usually referred to as "Saladin"—was the sultan of Egypt in 1174. He scored a number of wins against the European Crusaders but was eventually defeated by Richard the Lionhearted at the Battle of Arsuf in 1191. Saladin was held in great esteem in medieval Europe. Despite his resistance to Christianity, he was acknowledged for his piety and noble nature.   

In Roman mythology Latinus was the king of Latium, the region of central Italy in which Rome was founded. Lavinia was his daughter.  

Camilla was the daughter of Metabus, king of the Volscians. Metabus and Turns, king of the Rutulians, were the leaders of indigenous Italians who resisted invasions by the Trojans. Penthesilea was the queen of the Amazons, a race of women warriors. She was killed by Aeneas as she fought to save Troy. These events, which are described in The Aeneid, are so old as to be more mythical than historical in nature.

"Electra" here is not a reference to the daughter of Agamemnon and Clytemnestra, the Electra made famous by Sophocles and Euripides. Rather, it is a reference to the daughter of Atlas and the mother of Dardanus, founder of Troy. Her descendants include Aeneas and Hector. 

In this scene Dante includes himself among the "band" of poets he considers the six greatest in history. While this inclusion may seem hubristic, Dante would have considered his talent a gift from God, not something he achieved on his own. In the poem, Dante is chastising those who have wasted God's gifts; he can at least claim that he is not doing so with his own. In Paradise Lost, Milton makes the same argument but even more forcefully. 

"Naso" is Publius Ovidius Naso, the Roman poet best known as Ovid (43 BCE – 18 CE). Ovid's most influential poem was the epic Metamorphoses, which Dante references heavily. 

"Lucan" is the Roman poet and historian Marcus Annus Lucanus (39–65 BCE). Lucan is the author of Pharsalia, an epic bout the conflict between Caesar and Pompey.  

"Flaccus" is Quintas Horatius Flaccus (65–8 BCE), a Roman poet. In the Middle Ages he was known mostly for his satires, though he also wrote odes. Flaccus describes himself as a satirist in *Ars Poetica. *

Here, Virgil is paying his respect and indebtedness to Homer, from whose works (The Odyssey and The Iliad) Virgil heavily borrowed. Dante himself could not read Greek and thus his knowledge of the works was only indirect. 

In the Bible, Jacob's name was changed to "Israel" (Hebrew for "struggles with God") after he wrestled with an angel. Jacob's father was Isaac, the son of Abraham. Jacob married Rachel and had twelve sons who became the founders of the twelve tribes of Israel.