Alonso de Cárdenas, Grand Master of the Order of Santiago, erected this church in 1481, around the same time -1482- the church in Llerena was finished, where he is buried, together with his wife D.ª Leonor de Luna, on the Gospel side.
A singular characteristic of this temple, which distinguishes it from others of its style, is the great elevation of its pilasters, crowned by capitals of great simplicity, which lends the building an extraordinary sumptuousness. The main nave has pointed transversal arcades, with a large span, a wooden roof distributed in three sections, with the first section deviated from the main axis of the building. On its north front, there is a brick pointed arcade belonging to the primitive nucleus. In this chapel there are ribbed vaults with a star-shaped triplet. In short, two side chapels covered with star-shaped vaults, the Gothic arch of the presbytery, the slenderness of the building, of great elevation and elegance, and the simplicity of the capitals, allow us to place the oldest part in the 15th century, which coincides with the historical data. In the first quarter of the 16th century, constructions of notable interest were carried out, going from Gothic to Renaissance, as can be seen in the vault of the presbytery, and which show the presence of a master contemporary of Diego de Riaño. The doorway must have been built in the 18th century. In 1840 San Sebastián had six priests, a parish priest and a lieutenant, but in previous centuries it had a curate and eleven other clerics.
The Hermandad de Ntro. Padre Jesús Nazareno (Brotherhood of Our Father Jesus of Nazareth) was located in this church until it was closed for worship. Built in masonry and brick, its main nave, to which is attached another lateral nave on the left or Gospel side, of great elegance due to its great elevation, is divided into four bays, the first one deviated from the axis of the building by means of pointed transverse arches of great span that rest on pilasters attached to the wall, Until a few years ago, it was covered with a wooden roof, which has been replaced by the current gabled roof, which retains the memory of the original one in the use of the timbers. For its part, the presbytery, also deviated in relation to the longitudinal axis of the nave and accessed through a pointed triumphal arch with two simple mouldings, is covered with a star-shaped vault, made up of two diagonal ribs which, when joined together by means of other secondary ribs – the terceletes – form a four-pointed star, inside which a circle is inscribed.
The ribs that make up the vault we have just described show in their joints a series of rosettes decorated with interesting heraldic themes, which we have not been able to study properly due to their great height, but which perhaps allude to the Priory of San Marcos de León and the Order of Santiago, These ribs start from corbels decorated with reliefs representing the symbols of the Evangelists, joined together by means of imposts that only run along the side walls of the presbytery, disappearing in the front wall due to the placement of the altarpiece that once occupied its surface. In one of these side walls is the entrance to a small chapel, also covered with a star-shaped vault but with a much simpler design, similar to two harpoon points joined at their vertices.
Another chapel, which was once the Sagrario chapel, opens onto the first section of the nave, next to the main arch that leads to the chancel of the church. With a square floor plan, its roof is also a star-shaped vault with tercelets, whose masonry still shows remains of the Baroque pictorial decoration with which it was enriched in a later reform, perhaps from the 18th century, to which the half-barrel vault with transverse arches that covers the lateral nave must also correspond.
En definitiva, nos encontramos en el templo de San Sebastián con una combinación de elementos estilísticos del gótico, mudéjar, renacimiento y barroco. Esta iglesia fue cerrada al culto en el año 1936. Actualmente, está siendo usada como Mercado de Abastos.
