The redemption of captives has always been regarded in the Church as a work of mercy, as is abundantly testified by many lives of saints who devoted themselves to this task. The period of the Crusades, when so many Christians were in danger of falling into the hands of infidels, witnessed the rise of religious orders vowed exclusively to this pious work. In the thirteenth century there is mention of an order of Montjoie, founded for this purpose in Spain, but its existence was brief, as it was established in 1180 and united in 1221 with the Order of Calatrava. Another Spanish order prospered better; this was founded in the thirteenth century by St Peter Nolasco under the title of Our Lady of Mercy (de la Merced), whence the name Mercedarians. It soon spread widely from Aragon, and has still several houses at Rome, in Italy, Spain, and the old Spanish colonies. Finally, the Order of Trinitarians, which exists to the present day, had at first no other object, as is recalled by the primitive title: "Ordo S. Trinitatis et de redemptione captivorum". its founder, St. John of Math, a native of Provence and a doctor of the University of Paris, conceived the project under the pious inspiration of a pious solitary, St Felix of Valois, in a hermitage called Cerfroid, which subsequently became the chief house of the order. Innocent III, though little in favor of new orders, granted his approbation to this enterprise in a Bull of 17 December, 1198.

The primitive rule, which has been in turns mitigated or restored, enacted that each house should comprise seven brothers, one of whom should be superior; the revenues of the house should be divided into three parts, one for the monks, one for the support of the poor, and one for the ransom of captives; finally it forbade the monks when journeying to use a horse, either through humility, or because horses were forbidden to Christians in the Mussulman countries, whither the friars had to go; hence their popular name of "Friars of the Ass".

In France the Trinitarians were as much favoured by the kings as by the popes. St. Louis installed a house of their order in his château of Fontainebleu. He chose Trinitarians as his chaplains, and was accompanied by them on his crusades. Their convent in Paris is dedicated to St. Mathurin; hence they are also known in France as Mathurins. Founded in 1228, the Paris house soon eclipsed Cerfroid, the cradle of the Trinitarians, and eventually became the residence of the general, also called grand minister, of the order. Towards the end of the twelfth century the order had 250 houses throughout Christendom, where its benevolent work was manifested by the return of liberated captives. This won for it many alms in lands and revenues, a third of which was used for ransoms. But the chief source was collections; and to make these fruitful it was not considered enough to attach indulgences to the almsdeed, recourse was had to theatrical demonstrations to touch hearts and open purses. The misfortunes of the unhappy captives in the Mussulman countries were the readiest subjects for descriptions, sermons, and even tableaux. In Spain these alms-quests were made solemnly: the religious on their mules were preceded by trumpeters and cymbal-players, and a herald proclaimed the redemption by inviting families to make known their kinsfolk in captivity and the alms destined for their ransom.

From the fourteenth century the Trinitarians had lay assistants, i.e., charitable collectors, authorised by letters patent to solicit alms for the order in their respective towns; these were called marguilliers. There were also confraternities of the Holy Trinity, chiefly in the towns where the order had no convent; these consisted of lay tertiaries who wore the scapular of the order, were associated with its spiritual favours, and devoted a portion of their income to its work. In fact the Trinitarians had considerable resources to meet the needs of their work. The funds being collected, the ransomers to the number of three or four set sail from Provence or Spain with objects to alleviate the lot of the captives or coax their jailers. Their destination was usually the Barbary States, especially in the sixteenth century when the corsairs of Tunis, Algiers, and Morocco infested the Mediterranean and made plunder their chief means of existence. The Mercedarians went chiefly to Morocco, while the Trinitarians went preferably to Tunis or Algiers. There began their trials. They had to confront the dangers of the journey, the endemic diseases of the African coast, exposed to the outrages of the natives, sometimes to burst of Mussulman fanaticism, which cost several lives. The most delicate part of the task lay in the choice of captives amid the solicitations with which the monks were besieged and the negotiations for settling the ransom-price between the corsairs and the Trinitarians, between the exactions of the former and the limited resources of the latter. When the sum was not sufficient, the Trinitarians were held as hostages in the place of the captives until the arrival of fresh funds. The choice of captives was made according to the funds; ransom was first paid for the natives of the regions which had contributed to the redemption. Sometimes certain captives were previously indicated by their family who paid the ransom. When the captives returned to Europe, the Trinitarians had them go in procession from town to town amid scenery intended to impress the imagination in justification of the use of the alms and to inspire fresh almsdeeds. The number of those ransomed during the three centuries is estimated at 90,000. The most famous of these was Cervantes (ransomed in 1580), who at his death was buried among the trinitarians at Madrid in a habit of a Trinitarian tertiary.

Despite the large sums of money which passed through their hands, the Trinitarians had to struggle constantly with poverty. They had to defray the expenses of numerous hospitals, as well as to administer parochial charges. They suffered greatly in France during the English invasion of the fifteenth century and the wars of religion of the sixteenth. Moreover, there were conflicts between the Mercedarians, who had spread from Spain to France, and the Trinitarians, who had spread from France to Spain. They contested each other's right to collect and receive legacies: attempts at fusion failed, and their rivalry gave rise to numerous suits in both countries and to a whole controversial literature. Their poverty resulted in a relaxation of the rules which had often to be revised, and in divisions in the order. While one party followed the mitigated rule, there was a reform party which aimed at a return to the primitive observance. Thus arose the first schism in 1578 at Pontoise, which in 1633 succeeded in entering the mother-house at Cerfroid.

About the same time the Trinitarians of Spain formed a schism by separating from the Trinitarians of France under Father Juan Bautista of the Immaculate Conception; the latter added fresh austerity to their rule by founding the Congregation of "Discalced Trinitarians of Spain". This rule spread to Italy and Austria (1690), where the ransom of captives was much esteemed during the constant wars with the Turks. Hence the three congregations, which gave rise to regrettable dissensions. The Discalced also went to France, where they were suppressed by a Papal Bull in 1771. The division between those observing the mitigated and the reformed rule was terminated by uniting without fusing them under a common general. At this time also they began to lay claim in France to the title by which they have since been known: Canons Regular of the Holy Trinity. The Revolution of 1789 suppressed them in all the territories to which they had spread. Joseph II had already suppressed them in 1784 in Austria and the Low Countries. They have retained a few houses in Italy, Spain, and the Spanish colonies. At Rome, where the convent of St. Thomas was united with the chapter of St. Peter in 1387, the Trinitarians protested many times unsuccessfully against this spoliation, when on the occasion of the seventh centenary of the foundation of the order in 1898, the chapter of St. Peter's voluntarily restored it. But their chief house is the Basilica of St. John Chrysogonus which was given to them by Pius IX in 1856.

There have always been nuns attached to the hospitals of the order, but they do not seem to have formed an integral part of it. The true Trinitarian Sisters were founded in Spain by Maria de Romero in 1612 and they still have convents at Madrid and in other cities. They form part of the discalced congregation.

The Trinitarians wear a white habit, with a cross of which the upright is red and the cross bar blue.

CH. MOELLER