The Monarca was a 74-gun third-rate ship of the line of the Spanish Navy. She was ordered by a royal order of 28 September 1791, built in the Reales Astilleros de Esteiro shipyard and launched on 17 March 1794. Designed by Romero Landa and belonging to the Montañés-class (a subset or modification of the San Ildefonsino class), her guns were distributed along two decks, with 28 24-pounder in his first battery, 30 18-pounders in her second battery, 12 8-pounders on her upper deck and four 8-pounders on her bowcastle.
She underwent proving trials between September and November 1794 alongside the Montañés, also launched in 1794, aiming to work out whose method of construction was best. The trials were overseen by José Justo Salceno and the results favoured the Montañés. The Monarca was assigned to Juan de Lángara's squadron, taking part in the defence of Roses.
She took part in the battle of Trafalgar on 21 October 1805 under the command of captain Teodoro Argumosa. She was attacked at close range by Mars and Tonnant as they first cut the Franco-Spanish line. The ship behind the Tonnant, the Bellerophon, slipped under her stern at 12:30 and fired two broadsides into her. She was heavily damaged, with 100 men killed and 150 wounded. A party of 55 Royal Marines captured the ship, but the night after the battle the surviving Spanish crew overpowered them and cast them adrift, leaving them to the mercy of the storm that night.
On 24th October the survivors decided to try to repair the ship's rudder and return to Cadiz, as the weather was improving, but an hour later they were pursued by Leviathan, which also picked up the marines and some Spanish survivors of the storm. On 28th October the ship ran aground on the Arenas Gordas coast near Huelva, between Torre de la Higuera and Torre del Asperillo, leaving it lying on its side. On 31st October she was destroyed by the guns of the frigate Naiad to avoid her being reused or refloated.