Erected between 1756 and 1767, the St Louis Church in Kraslaw is a unique historical and artistic monument. It was founded by the owners of Kraslaw - Count Konstantin Ludwik Plater of Broel and his wife, Augusta of Oginskis - as the seat of the Livonian bishops. The Plater family also owes the construction of the Decimal Sminarium, for the upkeep of which the Livonian Bishop Teodor de Ludingshausen-Wolff, a descendant of the former owners of Kraslaw, donated a fund as early as 1711. Further funds were provided by bequests from noble families and from the bishops of Livonian Anton Ostrowski and Smolensk bishop George Mikolaj Hylzen. The foundation was approved by an act of the Sejm of 1768.

Diocesan Seminary in Kraslaw (Krāslava)
. The ceremonial opening of the Seminary took place in 1757, still at the old wooden church, which was erected in 1676 through the efforts of the Jesuit George de Ludingshausen-Wolff, then owner of Kraslaw. After the new St Ludwig's Church was consecrated, the old church was moved to nearby Kombula, where it served the faithful as a branch church of the Kraslaw parish. The seminary was run by Lazarists brought from Warsaw, priests from the Congregation of the Missionaries of St Vincent de Paulo, invited to Kraslaw by Bishop Antoni Ostrowski (1755). The Jesuit mission was moved to Indrycy in 1756, and the Lazarists also took over the schools they had founded.

The Kraslaw seminary, also known as the 'papal' seminary because part of the funds for its upkeep were provided by the Holy See, existed for 86 years and educated 253 priests. Its situation worsened after 1772, when, after the First Partition of Poland, Kraslaw found itself within the borders of the Russian Vitebsk Governorate. In 1844. The seminary was moved to Minsk. This was also the end of the activities of the priests of the Congregation of the Missionaries of St. Vincent de Paul in Kraslaw. Until 1864, sisters from the female branch of the congregation were still working here, whose convent was opened in 1779 thanks to Augusta, née Oginska, wife of Konstanty Ludwik Plater.

St Louis Parish Church in Kraslaw (Krāslava)
. Although St Ludwig's Church in Kraslaw was not destined to serve as the cathedral of the Inflantine bishops for too long and remained only a parish church, this does not detract from its importance as an outstanding work of architecture. The designer of the new church, built between 1755 and 1767, was the architect Antonio Paracco. This was not his only project in Inflants, where he eventually settled permanently. He designed, among others, the Plater Library in Kraslaw, as well as the Dominican Church in Drua and the Holy Trinity Church in Oshvoy (possibly also the Church of the Assumption of the Blessed Virgin Mary in Przydruisk).

The Kraslaw church was consecrated in 1777 by Mogilev's first archbishop, Stanislav Siestvensky. He was also present at the celebrations in 1784 for the transfer of St Donatus' relics to the new chapel, built at the Church of St Louis with funds from Augusta of Oginske Plater. The Plater family had brought the relics of the martyr from the catacombs of St Lawrence in Rome as early as 1778, but they were initially housed in the palace chapel.

The decoration of the Baroque interior of St Louis Church was a turn towards classical solutions. It lacked rich ornamentation or stucco decoration, abandoned in favour of ordered architectural motifs. The composition of the monumental main altar was subordinated to the painting on the wall in the central niche. The author of the fresco depicting King Louis the Saint was the Italian painter Filippo Castaldi (Gastaldi, Gastoldi, Gustelding) (1730-1814). In addition, between 1760 and 1762, Castaldi produced six more altarpiece compositions using the al fresco technique: St Peter and St Paul, St Vincent de Paul, St Anthony, the Holy Trinity, the Assumption of the Virgin Mary and the Assumption of the Blessed Virgin Mary. Also of his authorship are the portraits of the church's founders, Konstanty Ludwik Plater and his wife Augusta, née Oginskis, now displayed in the church choir. These paintings used to decorate the interior of the Plater family's library in Kraslaw.

After 1884, Castaldi's fresco, deteriorating due to Kraslaw's humid climate, was replaced by a monumental oil painting with similar content: Saint Louis setting out on a crusade. Thanks to the initiative of Eugeniusz Plater (1826-1916), this canvas was commissioned from the Krakow master Jan Matejko by the last rector of the seminary and later parish priest and dean of Kraslaw, Father Jozef Yalowiecki (18171885), supported financially by the Plater family.

Conservation work
In 2003, conservation work began in the Church of St Louis. The conservation of the oil painting from the main altar, which took place between 2003 and 2005 under the direction of Józef Steciński, was an extremely difficult undertaking. The dean and parish priest of St Ludwig's Church, Monsignor Jozef Lapkowski (Jazeps Lapkovskis) (1920-2005), who rendered great service to Kraslaw, had been striving for it for years. The organisational side of the project was handled by the Centre for Polish Cultural Heritage Abroad of the "Polish Community" Association. The work at St Ludwig's Church was carried out in consultation with the Latvian State Inspectorate for the Protection of Cultural Heritage (Valsts kulturas pieminekl u aizsardzibas inspekcija), with the assistance of the Polish Embassy in Riga, as well as the parish priest and parish council and Kraslaw town authorities.

The conservation of the giant canvas Saint Louis setting out on a crusade (unframed the painting measures 695 x 328 cm) was funded by the Senate of the Republic of Poland and the Ministry of Culture and National Heritage. The conservation work started in 2003, carried out by a team of conservators under Steciński's direction, and preceded by expert reports and chemical and microbiological tests, confirmed the urgent need for specialist intervention, which had previously been indicated by damage to the paint layer, canvas and frame caused by damage from the Second World War, the damp climate and the church's inadequate ventilation.

The conservation of the historic picture frame was carried out by Jozef Stecinski with funds provided by the Latvian State Inspectorate for the Protection of Cultural Heritage. Thanks to funds provided by the Latvian side, art conservator Kristīne Širvinskas restored the wall painting by Castaldi, which had been discovered on the wall enclosing the presbytery. By decision of the church authorities, the oil painting of Saint Louis setting out on a crusade was moved to the south wall of the presbytery. Castaldi's fresco is on display in the main altar. The conservators also looked under the paintings of the side altars. Traces of wall paintings were discovered there too.

Father Łapkowski died shortly before completion of the conservation of the painting "according to a sketch" by Jan Matejko. After his death, the historic shrine and St Louis parish in Kraslaw were looked after by Father Martins Kluss, whose pastoral duties were taken over by Father Edward Voroneckis (Eduards Voroneckis) in January 2006.

The cooperation with St Ludwig's parish, which was continued by the Ministry of Culture and National Heritage, resulted in the discovery of more Castaldi paintings and the full conservation of the main altar, which was carried out by a Polish-Latvian team of conservators led by Tomasz Dziuravec, and on the Latvian side by Dmitrijs Laščetko. Funding for the project was provided by funds from the Programme of the Ministry of Culture and National Heritage.

Through the 12-year-long project, started in 2003 and ceremonially completed in 2015, thanks to the support and involvement of many people and institutions from both countries, it was possible to restore one of the most beautiful and valuable monuments of the common Polish-Latvian cultural heritage. The project was made possible thanks to the support of the Ministry of Culture of the Republic of Poland, the Ministry of Culture of the Republic of Latvia, the Embassy of the Republic of Poland in the Republic of Latvia, the Latvian State Inspectorate for the Protection of Cultural Heritage, the Latvian State Fund for Cultural Support, the "Polish Community" Association, Bishop Jānis Bulis of the Diocese of Rezekneńsko-Aglońska, priests of the St. Louis Church in Krasław, local government authorities, and the close cooperation of Polish and Latvian conservationists.