The Gothic, two-story chapel, which is part of the Gothic castle built by King Casimir the Great, was constructed in the second half of the 14th century. As a royal chapel, it primarily served the needs of monarchs who frequently stayed there, particularly during the Jagiellonian dynasty. During his 48-year reign, Władysław Jagiełło visited Lublin 35 times, and in 1386, at a gathering of the Crown nobility, he was elected King of Poland. He was the one who gave the temple its royal character. At his command, in the early 15th century, Ruthenian painters under the direction of the little-known master Andrzej covered the chapel’s interior with Byzantine-Ruthenian murals.

In the 16th century, the building received a Renaissance portal, and in the 17th century, the front façade was adorned with a gable in the Lublin Renaissance style. During the Sejm (Parliament) of 1569, where the Union of Lublin was signed, King Sigismund II Augustus resided in the castle for several months. On June 29, 1569, a solemn thanksgiving service was held in the chapel. Dates carved into the chapel walls and an inscription on the staircase leading to the choir—unia facta est cum Ducatus Lytwanie (the union was made with the Grand Duchy of Lithuania)—confirm the event. In the 17th century, during the Swedish and Cossack wars, the castle suffered destruction, but the Chapel of the Holy Trinity and the late Romanesque tower from the 13th century survived.

In the 1820s, the former royal castle was replaced with a neo-Gothic prison building. During this reconstruction, the medieval murals were covered with layers of plaster and whitewash.

The castle church belongs to the type of two-story, single-pillar temples common in medieval Latin Europe. The division into floors was dictated by its function as a royal chapel. The liturgy involving the king or members of the court was held in the upper church. In the Lublin chapel, the lower level served as a facility for clergy. Steep stairs built into the thick walls of the northern and southern sides provided access between the floors.

The upper chapel consists of a square nave and an elongated, polygonal presbytery. At the center of the nave stands an octagonal pillar supporting a stellar vault. A simple, pointed triumphal arch separates the nave from the presbytery. Both floors have an identical spatial layout characteristic of late Gothic architecture. Structural solutions, ribbed vaulting, brackets, pointed-arch windows, and portals confirm the chapel’s affiliation with Western European culture. However, its painted decoration belongs to the Byzantine artistic tradition, following a sacred iconographic canon established over centuries.

In Byzantium, mural paintings were closely integrated with architecture, complementing its symbolism through visual imagery. The paintings were arranged according to a hierarchical system: the church interior was seen as a reflection of the Cosmos created by God. A fixed iconographic program determined the placement of themes: the eternal glory of God in the dome’s apex, below it a row of prophets and an evangelical cycle in the nave, and Eucharistic themes in the presbytery. Secondary narratives, typically scenes from the lives of Christ, Mary, or the saints, were developed in the lower zones of the interior. The central column—symbolizing the pillar of heaven—expressed the connection between the earthly and divine realms.

The iconographic program of the Chapel of the Holy Trinity in Lublin, inspired by Byzantine traditions, was adapted to fit its non-domed architectural structure. The polychrome paintings were executed following Byzantine technical traditions. A plaster mixture of lime and finely cut fibers was applied in sections that the painter could complete in a single day. Drawings on the wet, smoothed plaster were reinforced with engraved contours. Mineral pigments mixed with water were used for painting, with crystallized calcium carbonate from the drying plaster acting as the binding agent.

A preserved fragment of a foundation inscription in Old Church Slavonic enables precise dating of the polychrome completion to the feast of St. Lawrence, August 10, 1418, and reveals the name of the master responsible—Andrzej. During conservation work, the names Kurył (Cyril) and Juszko were identified as painters who contributed to the chapel’s murals. Stylistic and workshop features suggest ties to the Tver and Novgorod schools, with noticeable Balkan influences in many scenes, particularly those of the Passion.

In 1899, the Lublin-based painter Józef Smoliński noticed fragments of polychrome paintings beneath the peeling whitewash layer. He uncovered a scene on the staircase enclosure leading to the gallery, making a copy and description of it, correctly identifying the depiction as that of the murals’ patron. Smoliński’s discovery attracted the attention of the Academy of Learning in Kraków and the Imperial Archaeological Commission in St. Petersburg.

The first conservation efforts on the polychrome paintings began in 1917. However, events during World War II and the postwar decades significantly contributed to their deterioration. In 1976, a comprehensive project was launched to secure the chapel’s structure and restore the paintings. The original murals were revealed from beneath multiple layers of repainting, repairs, and plaster patches. This extensive conservation work was completed in 1997.