She was born late 1462 or early 1463, an illegitimate daughter of Galeazzo Maria Sforza, Duke of Milan, by Lucrezia Landriani. The Duke legitimised her and brought her up with his legitimate children. Lucrezia Landriani seems to have been generous with her favours as she had children not only by her husband, but by the Duke and others. At the age of nine she was engaged to Girolamo Riario who was brutal, cowardly and probably the son of Pope Sixtus. They married in
February 1477 and she departed for Rome. The 14-year-old bride---tall, slim, blond and very attractive---was received with ceremonies and banquets.
Girolamo Riario was made Captain General of the Church and commander of the Castel Sant' Angelo. Fat, Lazy, arrogant and suspected of numerous murders, he had to have an armed escort when going out. Even though it seems unlikely that she loved her husband, they had seven children.
In 1484 Pope Sixtus died and, in the turbulence that usually followed a pontiff's death, she took control in the name of her absent husband of the Castel Sant' Angelo. The garrison obeyed her even though she was only twenty-one years old and seven months pregnant. She remained in charge for thirteen days and, when she realized she was without her husband's support, surrendered the fortress to the cardinals.
With her husband she went to Forli to rule Imola and Forli where they built a palace. Girolamo tried to make himself popular by paying his soldiers well and reducing the taxes for his people, but only to run out of money. Then he made himself hated and feared by all, including his wife Caterina Sforza, by raising the taxes and confiscating properties.
While they were at Imola in 1487, a few people in Forli tried to rise against them and, as Girolamo was ill, Caterina went back to Forli where she had six rebels decapitated in the city square.
However, this was not the end of the uprisings against Girolamo Riario; on 14 April 1488 Cecco Orsi, captain of Riario's guard, together with two accomplices murdered the forty-five-year-old tyrant. According to legend, Caterina Sforza locked herself and her children in her room but Cecco Orsi soon had them extricated. However, she had been able to instruct Tommaso Feo, who was in control of the citadel of Ravaldino, not to surrender no matter what even she would
say later on. Whoever was in control of Ravaldino would be in control of Imola and Forli. She was taken to the castle's walls imploring Tommaso Feo to surrender; but his reply was that Cecco Orsi, for fear of her brother the Duke of Milan, would not dare harm her.
A second time Caterina was taken to the citadel and this time she pursuaded her captors to allow her to enter the castle with the pretext of pursuading Tommaso Feo in person to surrender, as her
children were being held as security for her return. However, once inside she refused to return and, when Cecco Orsi threatened to kill her children, she stood on the castle wall and lifted her skirts to display "the mould for casting more". Realising he was outwitted, Cecco Orsi fled.
Back in control, Caterina pursued and arrested as many conspirators as possible. As well, she vowed to hang anyone who had ransacked the Riario palace unless they restored the booty. Consequently, Cecco Orsi's aged father was executed.
She was regent for her eldest son, Ottaviano; but as he, too, was fat and lazy she continued ruling Imola and Forli even when he came of age. As lover she had taken Tommaso Feo's younger brother, Giacomo, and secretly married him. He was beautiful and only twenty years old.
Later he was made vice-regent of Imola and Forli, only to become arrogant and resented by the population. Perhaps he felt secure as Caterina had become pregnant and later produced a son, Bernardino.
One day, Caterina with her children---Ottaviano, Cesare and Bianca---went hunting with Giacomo Feo. However, they were waylaid and Giacomo Feo was murdered. The chief murderer, Gian Antonio Ghetti, maintained that Caterina and Ottaviano had ordered the murder and he may well have believed this, but Caterina took revenge. Ghetti was killed and his wife and two small children were thrown into a spiked well. Altogether forty people, guilty or innocent, were killed.
The 28-year-old Giovanni de' Medici then came to Forli and became Caterina's lover, political advisor and ruler of Forli. Again she married him secretly and another son, Giovanni delle Bande Nere, was born. However, only a year later, Giovanni died. Alone she continued to rule Imola and Forli.
In 1499 Cesare Borgia began his quest for a state for himself. Supported by his father, Pope Alexander VI, he attacked Forli. Caterina tried to defend herself but failed in an attempt to poison
the pope. Her children were taken for safe-keeping in Florence while she built up the security of Ravaldino. She also took hostages from local prominent families she expected to be hostile to her.
The city of Imola surrendered first to Cesare Borgia and then was followed by Forli. However, Caterina refused to surrender Ravaldino. Cesare placed a price on her head of ten thousand ducats, dead or alive; her answer was a price on his head of ten thousand ducats alive, but only five thousand for a dead Cesare.
The siege began on 19 December 1499 and lasted for twenty-four days in terrible winter weather. Wearing armour, Caterina took part in the defence. Entering Ravaldino, Cesare's army slaughtered the defenders. Caterina was captured and raped by Cesare who boasted that she had
been more determined in the defence of Ravaldino than in the defence of her virtue. He then raped her several times more before locking her up in the Vatican. When she attempted to escape, she was locked up in Castel Sant' Angelo. A prisoner for almost sixteen months, French pressure eventually secured her release. Having been in damp and ilthy dungeons with insufficient food, she was now thin and haggard with her hair turning white.
She went to Florence where she died eight years later of a liver ailment, peritonitis and pleurisy. She was forty-six.

Source: Leo van de Pas