Short answers, pulled from the story.
The Aventine Hill is the southernmost of Rome's seven hills. It has two distinct summits, Aventinus Major to the northwest and Aventinus Minor to the southeast, divided by a steep cleft. It belongs to the modern twelfth rione, or ward, of Rome, known as Ripa.
Around 493 BC the Roman Senate built a temple on the Aventine for Ceres, Liber, and Libera, the patron deities of the plebs. A law around 456 BC granted plebeians formal property rights there. The hill was also the base for plebeian aediles and tribunes who rose to prominence in Republican politics.
In the standard founding myth, Remus set up his augural tent on the Aventine while Romulus chose the Palatine. Remus saw fewer auspicious birds than his brother and lost the right to found the city. The scholar Skutsch in 1961 argued that an older variant by the poet Ennius placed Romulus on the Aventine instead, with Romulus later reassigned to the Palatine by tradition.
When Alaric I sacked Rome in 410 AD, the Aventine Hill was totally destroyed. Ancient sources suggest its near-total ruin was a direct consequence of its having become a concentration of aristocratic residences during the imperial era.
After the murder of the Socialist deputy Giacomo Matteotti, opposition members of parliament withdrew to the Aventine Hill and refused to take their seats in a protest called the Aventine Secession. The action ended their formal participation in parliament and their political activity. The term consciously echoed the plebeian secessions of ancient Rome.
In the Falco series by Lindsey Davis, the Aventine is portrayed as a rough working-class district of ancient Rome. The protagonist Marcus Didius Falco is a private informer who lives on the Aventine and occasionally works for the emperor Vespasian.