It has been established that Cesare Borgia was born in Rome—in 1480—the illegitimate son of Cardinal Roderic Llançol i de Borja, (usually known as Rodrigo Borgia), later Pope Alexander VI, and his mistress Vannozza dei Cattanei, about whom information is sparse. The Borgia family originally came from the Kingdom of Valencia, and rose to prominence during the mid-15th century; Cesare's grand-uncle Alphonso Borgia (1378 – 1458), bishop of Valencia, was elected Pope Callixtus III in 1455. Cesare's father, Pope Alexander VI, was the first pope who openly recognized his children born out of wedlock.
Being the second son of Rodrigo Borgia, Cesare was groomed for a career in the Church. At the age of 13, he was made Bishop of Pamplona. Following school in Perugia and Pisa, Cesare studied law at the Studium Urbis (nowadays known as the Sapienza University of Rome). After his father's elevation to Pope, Cesare was made Cardinal in 1495 at the age of 15, at the time the youngest to have been appointed.
According to the journal of Cardinal ** Sforza, Cesare Borgia and his friend, Giovanni Farnese, were admitted to the College of Cardinals on the 3 February 1495.
Cesare first met Arthur during the young Angevin king's visit for his coronation. Almost immediately, the two became close friends.
Having spent most of 1496 in France in the company of his brother-through-marriage, Arthur, Cesare became increasingly disillusioned with the Catholic Church and his role as Cardinal. The death of his older brother, Giovanni, made his decision clear. On the anniversary of his appointment as cardinal, Cesare demanded his removal from the College of Cardinals to which his father was forced to agree. To maintain some amount of control, Pope Alexander VI made Cesare Prince of the Romangna (and papal gonfaloniere) soon thereafter and tasked him with subjugating the de facto independent vassals that had left during the papacy of Pius III. Finally, Cesare had the opportunity to prove his worth as both a warrior and diplomat.
By late in autumn of the year, Cesare along with Orsini had reconquered up to the borders of San Marino.
The Ordelaffi family proved to be a stalwart obstacle in reclaiming the Romagna completely due in large part to their marriages into the Sforza family. The ever-growing interest of the Empire in northern Italian affairs did little to help the situation. Cesare remained focused on his goal of reclaiming the Romagna.