Originally protected by the Byzantine navy, the Papal States found itself in need of a naval force of its own following a Muslim raid on Rome in 843 and the sack of the city's basilicas extra muros in 846.

[5] In 1241, amidst the Guelphs and Ghibellines War and the papal election, Emperor Frederick II dispatched a combined Imperial-Pisan fleet of 16 galleys to Civitavecchia as part of an intense coercion against the conclave of the College of Cardinals - he simultaneously surrounded the city of Rome with Imperial soldiers.

[5] In 1244, Pope Innocent IV - lacking an independent maritime capability - asked his Lombard ally Genoa to ferry him to France to secure French support against the continued encroachments of the Emperor.

In response, Pope Calixtus III established a shipyard on the Tiber River and rapidly assembled a papal fleet of galleys and transports (roughly 60 ships in all).

[3] In 1456, this fleet departed (carrying 300 cannons and 5,000 papal soldiers) for the Aegean Sea, where it spent three years in regular combat with the Ottomans.

[5] Although this crusade was a success, the four papal galleys had all abandoned the fighting early because of concerns regarding the ongoing Black Death, which caused Ferdinand I of Naples to send his ambassador to Civitavecchia to demand the pope to explain the papal fleet's departure and formally dissolve their league of alliance (Pope Sixtus IV had intended for the crusading forces, upon liberating Otranto, to sail to and liberate Ottoman-held Vlorë as well).

[5] In 1496, a fleet of Venetian galleys and three Spanish ships commanded by Cesare Borgia (Alexander VI's son) arrive in Civitavecchia to reinforce the papacy during a period of pro-French unrest.

[5] Alexander VI soon ordered the Papal Navy to be revived, commissioning a modest fleet to engage in coastal patrol.

[5] Following the loss of Rhodes to the Ottomans, from 1523 to 1530, the Navy of the Knights Hospitaller was stationed in Civitavecchia alongside the Papal fleet, before the Order established itself in Malta.

[3] In 1535, the papal navy again supplied its 12 galleys to the Charles V's Holy League, which numbered 398 ships (including the 366-gun Portuguese São João Baptista) and roughly 30,000 soldiers in total.

[5] In 1571, Pope Pius V, determined to break the Ottoman fleet's grip on the Mediterranean, organized the Holy League - a military alliance between the Papal States, Spain, Venice, Genoa, the Knights of St. John, Tuscany, Savoy, Urbino, and Parma.

After almost a year of internal squabbling, the Holy League attempted to repeat their success in September 1572 by besieging the new Ottoman fleet at Navarino.

The Christian fleet made several unsuccessful attempts to enter the harbor of Modon, which failed because of the strength of the Ottoman's defenses, especially in the overlooking castle of Navarino.

[5] During Jubliee Year 1650, the Papal Navy remained on patrol in Civitavecchia to defend pilgrims from the threat of Ottoman raiders.

[5] After the death of Innocent X, the conclave decided to increase the papal fleet and dispatch it to defend the Kingdom of Candia on Crete, which was then in the midst of war with the Ottomans and at serious risk of collapse.

In 1684, following a visit and a blessing from Pope Innocent XI, the papal fleet of 10 galleys departed Civitavecchia to participate in the Siege of Santa Maura and the capture of Preveza Castle.

[5] In 1696, the Papal Navy participated in the Battle of Andros, sending a number of ships to support the combined Venetian and Maltese fleet.

At the beginning of Clement XI's pontificate, the papal navy is ordered to expand its patrol area to run from the Strait of Messina to Montecristo.

[5] Just over one month after receiving these frigates, they were sent on patrol, where they surprised and routed a band of Barbary xebecs and pinks who were preparing to attack a merchant fleet.

[5][3] After a brief period of naval expansion under Popes Benedict XIV and Clement XIII, the Papal Navy slowly withered until, by 1780, it consisted of just three galleys and two corvettes, and its mandate was confined to coastal patrol.

[5][3] In 1799, the Sanfedismos invaded Napoleonic Rome, liberating the Papal States and restoring pontifical sovereignty over the papacy's ports.

One was captured by Muslim pirates in 1826, but following a show of force by two frigates and a sloop-of-war from Piedmont under Captain Arnous, the Bey of Tripoli freed the ship with 10,600 francs compensation.

[7][12] In 1840, Lt. Col. Alessandro Cialdi directed an expedition to Egypt to retrieve several alabaster monoliths - gifts from the Egyptian Pasha to the pope.

As part of his break from the diplomatic policies of Pope Pius IX, Leo XIII sold off the last ship in the Papal Navy, the corvette Immacolata Concezione, during his first year in office.