When the revolutionaries sheared her sister’s hair, shackled her, and led her to the guillotine in October 1793, Maria Carolina of Austria did not merely grieve. She wrote a promise on the portrait of Marie Antoinette that she kept in her room: “I will avenge my sister. ” The words were not idle sentiment. From that moment, the Queen of Naples bent every nerve of her formidable will toward one end, and her fury would cost thousands of lives before it was spent.

To understand how Maria Carolina became the woman who would execute a hundred Republicans in cold blood, one must begin much earlier, in the nursery of the Habsburgs. She was born in 1752, the sixth child of Maria Theresa, Queen of Hungary, and Francis I, Holy Roman Emperor, to survive infancy. In an age when infant mortality swept through even the grandest palaces, the children who lived clung to one another with unusual closeness. None were closer than Maria Carolina and her younger sister Marie Antoinette, born three years apart.

Their fates seemed intertwined, and the two girls were inseparable. In 1767, when Maria Carolina was fifteen and Marie Antoinette twelve, their mother decided the bond had grown too strong. Maria Theresa, displeased with the girls’ behavior, insisted they be separated and raised apart. It was a tearful farewell, but worse news was already in motion.

Her parents had negotiated a marriage alliance with Spain, and Maria Carolina was to wed King Ferdinand IV of Naples. She complained and begged, but her protests meant nothing. On April 7, 1768, the wedding would take place whether she liked it or not. The groom, however, did not bother to attend his own ceremony.

Ferdinand IV sent a proxy—Maria Carolina’s own brother stood in his place. Any hope that the king’s absence might delay the marriage was dashed; the union was sealed regardless. Afterward, Maria Carolina traveled with her ladies, her brother, and his wife toward Naples, taking her time, lingering in Bologna and Florence. But when she crossed into the Kingdom of Naples, she had to dismiss her attendants and finally meet her husband more or less alone.

Her first impression was brutal. She found Ferdinand, in her own words, very ugly. After she had settled in somewhat, she softened enough to write: “I love him out of duty. ” Ferdinand’s opinion of his bride was no kinder.

After their first night together, he described her with the delicacy one might expect of a street urchin: “She sleeps like the dead and sweats like a pig. ”

Whatever they thought of each other’s looks, something between them worked in the dark. Their nights were lusty enough to produce eighteen pregnancies, though only seven children survived. Part of the reason may have been that they had nothing else to do together.

They shared no common language. Maria Carolina spoke German and some Italian, while Ferdinand spoke no German and not even proper Italian. He preferred the company of local street youths and had picked up their dialect instead. His behavior confirmed her low opinion.

Ferdinand was a teenager who seemed to resent the privileges of his position and expressed it in revolting ways. He ate spaghetti rudely during the opera and took open pleasure in conducting his morning bowel movements in front of his servants, even asking them to examine the results. He had received a poor education and was ill-prepared for kingship. In practice, he relied on his father’s Spanish council to run the kingdom, with Bernardo Tanucci at its head.

Tanucci paid the teenage queen little mind. That would prove to be a grave mistake. Maria Carolina, under the strict direction of her mother, had a secret plan. She intended to take Ferdinand’s power for herself.

The first step was winning his trust. She noticed that her husband had only one real interest: hunting. So she cultivated an interest in the sport, slowly and calculatingly ingratiating herself. Once she became his hunting companion, she moved swiftly into the Privy Council.

In 1777 she produced a male heir, which strengthened her position considerably. Ferdinand, for his part, gave up and admitted that his wife knew everything. Her next target was the Spanish council. She began at the top, with Tanucci.

She complained to Ferdinand that Tanucci sent letters with unpopular ideas, signing the king’s name, and making the king look foolish. The king fired him. Into the vacancy stepped the Marquis of Sambuca, a man loyal to Maria Carolina rather than to Spain. With the Spanish influence removed, Naples was freed from being little more than a Spanish province.

Her first mission was complete. She then brought her closest confidant, Sir John Acton, aboard as her assistant. Together, the two undertook an ambitious project: rebuilding the Neapolitan Navy, which Ferdinand and his council had neglected. They commissioned 150 ships and opened four marine colleges.

The partnership worked so well that tongues began to wag. By 1782, rumors spread that the queen and Acton must be lovers, despite there being no evidence whatsoever. Ferdinand, by now genuinely in love with his wife, believed the gossip and demanded proof. He made several attempts to catch them in the act, each one failing because there was nothing to catch.

Still, he flew into a rage and threatened both their lives. Maria Carolina, though innocent, hired detectives to trail her husband and learn how he planned to trap her. The castle became a farce of spies following a king who was hunting for a lover who did not exist. Eventually, the queen dismissed her detectives, and Ferdinand agreed to stop his paranoia.

But before the truce was complete, he demanded that Acton be sent away. She accepted, moving him to a neighboring town. The domestic drama, however, paled beside events unfolding in France. There, her beloved sister Marie Antoinette was queen to King Louis XVI, and the monarchy was collapsing under the weight of revolution.

Maria Carolina watched with alarm. She took immediate action to prevent a similar catastrophe in Naples. She divided the city into twelve wards, took control of the universities to suppress hostile intellectuals, created a secret police force, and hired spies to report what the people were saying and feeling. Though she had once favored free thinking, she now moved to stamp it out.

Her spies reported back a unanimous verdict: the people of Naples hated her across the board. Her sister’s situation was far more dire. Maria Carolina begged Marie Antoinette to flee France, but her advice came too late. On August 10, 1792, the people of Paris seized the queen and her husband, King Louis XVI, and took them into custody.

Maria Carolina refused to recognize France as a republic, nor would she acknowledge the French envoy, Armand, and his new legislation. Armand waited patiently for her recognition, but she was in no hurry, and their relations grew tenser by the day. Acton, now prime minister of Naples, stepped in as a go-between, supposedly to hold off a battle. But Acton was far from impartial.

Acting for Maria Carolina, he tried to double-cross Armand. The scheme came to light when Armand intercepted a letter Acton had written. Furious, the Frenchman began planning his revenge: nine ships, commanded by Admiral Latouche, were readied for Naples. When Maria Carolina learned of the approaching fleet, she panicked and made an astonishing about-face.

She recognized Armand and his republic immediately, hoping to avert the confrontation. But the nine ships had already sailed. On December 17, 1792, they arrived in Naples. Admiral Latouche issued a demand: Acton must apologize to him in person, or Latouche would destroy the city.

Everything she had built was suddenly at risk. She considered fighting, but when she met with her own admiral, she received shocking news: the navy she and Acton had rebuilt had not even been mobilized. There was nothing to fight with. She had to force Acton to apologize.

Once the apology was delivered, Armand sent his sailors—Republican agents in truth—ashore. Their mission was to stir up anti-monarchist sentiment in Naples, and they did so with ease. Maria Carolina needed to rid the city of these radicals. She turned to her chief of security, Luigi de Medici, a man she considered capable and trustworthy.

She dispatched him to locate and remove the troublemakers. But Medici brought in no radicals. It was not ineptitude. Medici was himself a Republican sympathizer.

He had tricked the queen and left her in dire danger. With her own security chief turned against her, Maria Carolina turned to France’s great enemy, Great Britain, and in 1793 she joined Naples to the First Coalition against France, alongside Britain, Austria, Prussia, Russia, Spain, Portugal, and Sardinia. The alliance, however, did nothing to save her sister. In October 1793, Marie Antoinette was sheared of her hair, shackled, and led to the guillotine, beheaded for treason among other charges.

The loss sent Maria Carolina into a hatred from which she never recovered. She stopped speaking French, calling it “that monstrous language,” and banned the works of French philosophers she had once enjoyed. Terror that the same fate might await her set in. She put the army on constant full alert, financing it with an unpopular tax increase.

She hired food tasters to check for poison and changed her sleeping location daily to avoid assassination attempts. The strain wore on her health. When Napoleon Bonaparte, the new French general, moved dangerously close to Naples, she could no longer bear the pressure. She agreed to pay France an indemnity in exchange for safety.

She married her son into Austrian royalty, joined an alliance with Austria against France, and then joined the Second Coalition, also against France. Paying off one enemy while arming herself against another was her way. The Second Coalition proved to be her undoing. Napoleon learned of her involvement and took it as a signal to act.

In January 1799, his forces occupied Naples. Maria Carolina and her family fled to Sicily. From exile, she organized an attempt to take the city back. In the summer of 1799, with the help of the English fleet, she accomplished the impossible: she defeated the French and returned to Naples in triumph.

She entered the city with her family, finally in a position to take her revenge. She did not hold back. She put a thousand Republicans on trial for treason. Of those thousand, one hundred faced the full force of her wrath.

They were executed, some by beheading, some by hanging. At last, she had avenged her sister. But her position was not stable. The people of Naples had endured occupation and upheaval, and they needed someone to blame.

They knew Maria Carolina, far more than the simple Ferdinand, called the shots. They blamed her. Though Ferdinand had done virtually nothing, at least he had not brought so much misfortune upon them. Her popularity sank to a new low.

More trouble was coming. Napoleon conquered Naples a second time. Maria Carolina and her family once again fled to Sicily, but this time her plans to recover the kingdom came to nothing. She went to Vienna, where on September 8, 1814, she died of a stroke.

She never saw Napoleon defeated, never saw her husband restored to the Neapolitan throne. But throughout her life, she had wielded power without apology and fought her battles to the bitter end, a force that even Napoleon himself acknowledged when he called her the only man in Naples.