After the First Punic War, Carthage is unable to fulfill promises made to its army of mercenaries, and finds itself under attack. The fictional title character, a priestess and the daughter of Hamilcar Barca, the foremost Carthaginian general, is the object of the obsessive lust of Matho, a leader of the mercenaries. With the help of the scheming freed slave, Spendius, Matho steals the sacred veil of Carthage, the Zaïmph, prompting Salammbô to enter the mercenaries' camp in an attempt to steal it back. The Zaïmph is an ornate bejewelled veil draped about the statue of the goddess Tanit in the sanctum sanctorum of her temple: the veil is the city's guardian and touching it will bring death to the perpetrator.
Chapter 1. "The Feast". During a victory banquet, the mercenaries destroy Hamilcar's garden for sport in his absence. Hamilcar's daughter Salammbô tries to quell the riot. Matho falls in love with her. The slave Spendius is released, and he tries to persuade Matho to take Carthage for the mercenaries.
Chapter 2. "At Sicca". The mercenaries leave the city unpaid and travel to Sicca. Later, Hanno comes and speaks to the mercenaries about delays in recompensing them, but he is driven off when Zarxas arrives and tells them of a treacherous massacre of 300 slingers who had stayed behind.
Chapter 3. "Salammbô". Hamilcar's daughter prays and is instructed by Schahabarim.
Chapter 4. "Beneath the Walls of Carthage". The mercenaries besiege Carthage; Matho and Spendius penetrate via the aqueduct.
Chapter 5. "Tanit". Matho and Spendius steal the Zaïmph. Because Matho is caught while breaking into Salammbô's bedroom to see her again, she falls under suspicion of complicity.
Chapter 6. "Hanno". The mercenaries leave Carthage and split into two groups, attacking Utica and Hippo-Zarytus. Hanno surprises Spendius at Utica, and occupies the city, but flees when Matho arrives and routs his troops.
Chapter 7. "Hamilcar Barca". The hero returns and an attempt is made to blame him for Hanno's losses. He defends himself before the Council and defends the mercenaries, but turns against the barbarians when he sees the damage they have done to his property.
Chapter 8. "The Battle of the Macar". Hamilcar defeats Spendius at the bridge of the Macar, three miles from Utica.
Chapter 9. "In the Field". Hamilcar's troops are trapped by the mercenaries.
Chapter 10. "The Serpent". Schahabarim sends Salammbô in disguise to retrieve the Zaïmph.
Chapter 11. "In the Tent". Salammbô reaches Matho in his tent at the encampment. Believing each other to be divine apparitions, they make love. The mercenaries are attacked and dispersed by Hamilcar's troops. She takes away the Zaïmph, and on meeting her father, Hamilcar has her betrothed to Narr' Havas, a mercenary who has changed sides.
Chapter 12. "The Aqueduct". The Carthaginians return to their city with the mercenaries in pursuit. Spendius cuts off the water supply to Carthage.
Chapter 13. "Moloch". Carthaginian children are sacrificed to Moloch. Hamilcar disguises a slave-child as his son Hannibal and sends him to die in his son's place.
Chapter 14. "The Defile of the Axe". The drought is broken and aid comes. Hamilcar drives the mercenaries away from their encampments. Later, thousands of mercenaries are trapped in a defile and slowly starve (the Battle of "The Saw"). Deaths of Hanno and Spendius, both by crucifixion.
Chapter 15. "Matho". Victory celebrations at Carthage. Matho is tortured before his execution; Salammbô, witnessing this, dies of shock. The Zaïmph has brought death upon those who touched it.

Question: How did Matho and Spendius get into Carthage?
Answer: They snuck in using the aqueduct.