The events unfolded in the aftermath of the tragedies (earthquakes, tsunamis, great fire) of 1755. In the social turmoil that followed, several shots were fired into a carriage, wounding the king. Pombal, the Secretary of State, rounded up "several of the most powerful and prominent nobles in Portugal. All were interrogated and many were tortured.” They were then tried, and executed on a platform in Belem before thousands of spectators.
“The Marchioness of Tavora was the first that was brought upon the scaffold, where she was beheaded at one stroke… [three noblemen and three servants] were strangled at a stake, and afterwards their limbs broken with an iron instrument. The Marquis of Tavora and the Duke of Aveiro [illustration] had their limbs broken alive… The body and limbs of each of the criminals, after they were executed, were thrown upon a wheel… But when Antonio Alvares Ferreira was brought to the stake, whose sentence was to be burnt alive, the other bodies were exposed to his view. The combustible matter which had been laid under the scaffolding was set fire to, [and] the whole machine with the bodies was consumed to ashes, and then thrown into the sea.”Unlike the French Revolution which lasted 11 months, the turmoil in Portugal continued for 18 years, from 1759-1777.
Quoted text (p. 351) from This Gulf of Fire: The Destruction of Lisbon, or Apocalypse in the Age of Science and Reason, by Mark Molesky. Illustration via Wikiwand.