One of ancient Rome’s most scandalous conspiracies unfolded in 63 B.C., when the senator Catiline attempted to mount an uprising against the Republic. Frustrated by a stagnating political career—he had twice failed to be elected consul—Catiline formed Rome’s malcontent aristocrats, downtrodden veterans and indebted poor into a rebel army. He planned to march on the city and murder its nobles, but his scheme hit a snag when Cicero—one of Catiline’s chief political opponents—caught wind of the conspiracy and publicly condemned him in a series of speeches on the Senate floor.

Under suspicion from his fellow politicians, Catiline fled Rome and rendezvoused with his forces in central Italy. The would-be rebellion was then publicly exposed in December 63 B.C., when a Gallic tribe turned on the conspirators and revealed their plans to Cicero. Armed with hard evidence of a plot, Cicero and the Senate oversaw the execution of several of Catiline’s cohorts and dispatched an army to intercept him in the field. In the ensuing battle, Catiline’s army was routed and he and many of his fellow conspirators were killed.

The illustrious Medici family ruled over Florence for some 300 years and helped fuel the Renaissance, but along the way they earned their fair share of enemies. Aggrieved by the family’s opposition to papal rule, in 1478 a group of conspirators led by Pope Sixtus IV, his nephew Girolamo Riario, the Archbishop of Pisa and others concocted an audacious scheme to wrest Tuscany from Medici hands. With the help of the Pazzi family—a rival Florentine clan—the group plotted to assassinate Lorenzo de’ Medici (also known as Lorenzo the Magnificent) and his brother Giuliano and then take charge of the city government.

The plan unfolded in grisly fashion on April 26, 1478. As the Medici brothers attended mass in the Duomo, they were set upon by two knife-wielding priests as well as a member of the Pazzi family and a hired assassin. Giuliano was stabbed some 20 times and killed, but Lorenzo managed to escape with only a shoulder wound. The larger coup failed to succeed after the botched assassination, and more than 200 conspirators were eventually captured and executed when an enraged citizenry rallied behind the Medici. When the dust finally settled, the Pazzi family had been stripped of their riches and permanently banished, leaving Lorenzo de’ Medici with almost total dominion over Florence.

To this day, Britons still celebrate Guy Fawkes’ Day, an informal holiday marking the anniversary of the doomed “Gunpowder Plot.” The scheme first materialized in May 1604, when a small cell of disgruntled Catholics led by Robert Catesby hatched a plan to assassinate the anti-papist King James I and install his daughter as a puppet leader. In March 1605, the conspirators rented a cellar underneath the House of Lords and filled it with three-dozen barrels of gunpowder. Their plan was as simple as it was outrageous: when Parliament opened on November 5, they would blow King James and his entire government sky high.

Unfortunately for Catesby and company, their plot was exposed at the eleventh hour after one of their members sent a letter to the politician Lord Monteagle warning him not to attend Parliament. Monteagle turned the letter over to the authorities, and on the evening of November 4 a search team discovered Guy Fawkes—the conspirator tasked with lighting the fuse—standing watch over the gunpowder. Fawkes revealed the entire plot under torture at the Tower of London, and by January 1606, Catesby and the other schemers had all been rounded up or killed. The survivors were later found guilty of high treason and hanged, drawn and quartered.

The little-known Newburgh Conspiracy unfolded in March 1783 as General George Washington’s battle-weary Continental Army wintered in a camp at Newburgh, New York. Despite having the upper hand in the Revolutionary War, Washington’s troops had grown frustrated with the fledgling Congress’ inability to compensate them with back pay and pensions. As the discontent spread, several high-ranking officers began circulating a letter written by an anonymous author calling himself “Brutus” (later revealed to be Major John Armstrong). The missive included a chilling suggestion: if Congress and the states would not pay up, the military might abandon the war effort and force their way into government coffers at gunpoint.

Though he was sympathetic to his soldiers’ plight, Washington knew that any uprising could have potentially disastrous consequences for the revolution. When the rabble-rousing officers met in an unsanctioned meeting on March 15, 1783, he made a surprise appearance and asked to address the crowd. After condemning the letter as unpatriotic and foolhardy, Washington urged the men to remain patient with Congress. Straining to read a letter near the end of his talk, he produced a small pair of spectacles and apologized, saying, “I have not only grown gray but almost blind in service to my country…” The impassioned speech paid off. Struck by Washington’s devotion to the war, the officers voted to put their “unshaken confidence” in Congress. Washington would go on to negotiate a ceasefire with the British only a month later.

John Wilkes Booth’s April 14, 1865 assassination of President Abraham Lincoln was just one part of a much larger plot to strike a decisive blow against the Union high command. The conspiracy had originated months earlier, when Booth and several other Southern sympathizers schemed to kidnap Lincoln and hold him ransom in exchange for Confederate prisoners. The plan encountered repeated setbacks, and as the rebellion disintegrated in April 1865, Booth was forced to alter his strategy. After learning that Lincoln and Union General Ulysses S. Grant were set to attend the play “Our American Cousin” at Ford’s Theater in Washington, D.C., he resolved to carry out a series of coordinated assassinations. Booth would personally murder Lincoln and Grant, while his co-conspirators George Atzerodt and Lewis Powell would kill Vice President Andrew Johnson and Secretary of State William Seward in their homes.

The conspirators hoped the killings would send the U.S. government into a tailspin, but their plan quickly fell apart. While Booth succeeded in mortally wounding Lincoln at Ford’s Theater, he missed out on Grant, who had decided not to attend the play. At the same time, Powell attacked Seward as the Secretary lay in bed, but only succeeded in leaving him with severe knife wounds. Atzerodt, meanwhile, abandoned the plan entirely and made no attempt to assassinate Johnson. While Lincoln would die the following morning, his administration remained intact. Within weeks, Booth had been killed and Powell, Atzerodt and several other conspirators were arrested. All were later executed or condemned to prison.

Adolf Hitler dodged several assassination attempts during World War II, but the most famous—and the closest to succeeding—came in 1944 in the weeks after the D-Day invasion. Convinced “Der Führer” was leading Germany to its doom, Lieutenant Colonel Claus von Stauffenberg, Colonel General Friedrich Olbricht, Colonel General Ludwig Beck, Major General Henning von Tresckow and others conspired to see him dead. As part of a plan dubbed “Operation Valkyrie,” the men plotted to murder Hitler and then use Germany’s reserve army to seize Berlin’s supreme command headquarters and stage a coup against the Nazi high command.

On July 20, 1944, Von Stauffenberg attended a military conference in Hitler’s “Wolf’s Lair” in Prussia armed with a bomb disguised in a briefcase. After placing the case near Hitler, he excused himself to make a phone call. The bomb successfully detonated at 12:42 p.m., but another officer had shifted the case behind a chair leg only moments before the explosion. While four other people were killed, Hitler escaped with only minor injuries. Operation Valkyrie crumbled with the news of his survival. Von Stauffenberg and Olbricht were promptly captured and shot, and Beck and Von Tresckow committed suicide. In the investigation that followed, Hitler saw that some 5,000 conspirators and suspected subversives were executed, many of them hanged with piano wire as a gruesome warning against future assassination plots.