The Mask of Zorro

In 1821, Don Diego De La Vega (Anthony Hopkins) fights against the Spanish in the Mexican War of Independence as Zorro, a mysterious swordsman who defends the Mexican peasants and commoners of Las Californias. Don Rafael Montero (Stuart Wilson), the governor of the region, learns of De La Vega's alter ego, and attempts to arrest him. De La Vega's wife is killed during the scuffle. Montero imprisons De La Vega and takes his infant daughter, ElÃ©na, as his own. Twenty years later Montero returns to California as a civilian, alongside ElÃ©na (Catherine Zeta Jones), who has grown into a beautiful woman. Montero's reappearance motivates De La Vega to escape from prison. He encounters a thief, Alejandro Murrieta (Antonio Banderas), who, as a child, once did Zorro a favor. De La Vega decides that fate has brought them together, and agrees to make Alejandro his protÃ©gÃ©, grooming him to be the new Zorro. Murrieta agrees to undergo De La Vega's training regimen in order to be able to take revenge on Captain Harrison Love (Matt Letscher), Montero's right-hand man, who was responsible for killing Murrieta's brother, Joaquin.
While still being trained, Murrieta steals a black stallion resembling Tornado from the local garrison. De La Vega scolds Murrieta, claiming that Zorro was a servant of the people, not a thief and adventurer. He challenges Alejandro to gain Montero's trust instead. Murrieta poses as visiting nobleman named Don Alejandro del Castillo y GarcÃ­a, with De La Vega as his servant, and attends a party at Montero's hacienda. At the party he gains ElÃ©na's admiration and enough of Montero's trust to be invited to a secret meeting where several other noblemen are present. Montero hints at a plan to retake California for the Dons by buying it from General Santa Anna, who needs money to fund his upcoming war with the United States.
Montero takes Murrieta and the noblemen to a secret gold mine known as "El Dorado", where peasants and prisoners are used for slave labor. Montero plans to buy California from Santa Anna using gold mined from Santa Anna's own land. De La Vega uses this opportunity to become closer to ElÃ©na, though he identifies himself as "Bernardo" the servant, learning that Montero told ElÃ©na that her mother died in childbirth. While walking in a market, ElÃ©na meets the woman who was her nanny. De La Vega sends Murrieta, dressed as Zorro, to steal Montero's map leading to the gold mine. Zorro duels Montero, Love, and their guards at the hacienda. When Zorro escapes, ElÃ©na attempts to retrieve Montero's map from the swordsman, but he seduces her, leading to a passionate kiss before he flees.
Terrified of Santa Anna's retribution if he discovers that he is being paid with his own gold, Montero decides to destroy the mine and kill the workers. De La Vega tells Murrieta to release the workers on his own so that De La Vega can reclaim ElÃ©na. Murrieta sets off, feeling betrayed by Diego's vendetta. De La Vega corners Montero at the hacienda and reveals his identity, but Montero captures him by threatening ElÃ©na. As he is taken away, De La Vega tells ElÃ©na the name of the flowers she recognized upon her arrival in California, convincing her that he is her father. She releases De La Vega from his cell and they proceed to the mine, where Murrieta and De La Vega defeat Love and Montero. ElÃ©na and Murrieta free the workers before the explosives go off, and then find the mortally wounded De La Vega. He makes peace with Murrieta before dying, passing the mantle of Zorro to him, and gives his blessings for his marriage to ElÃ©na. In a closing sequence they are shown to be living together with a son named Joaquin, in honor of Murrieta's brother.

Question: What did Murrieta steal?
Answer: A black stallion