The Church, comprising a single nave and a rectangular chancel, is located on a plot of land facing the Douro river, on a steep slope; therefore, the main façade is located at a lower ground level than the one of the chancel; this issue is internally compensated by the two steps that allow accessing the chancel through the nave.
It is on the outside that we are able to identify, in a more assertive way, the elements that allow us to state that this Church was built during a late Portuguese Romanesque period; it already features some components that would later characterise what has come to be called as the first rural Gothic style.
The main façade stands out immediately; it is organised according to four registers delimited by three frames placed in the continuity of the imposts found on the main portal, on the large upper window, and another one that is part of the window's base.
Adopting a very uncommon structure in the region, the façade is composed also by two overlapping openings - the portal and the already proto-Gothic rose window, formed by circles - in a composition that immediately refers us to a formal proximity with the Old Coimbra Cathedral.
The sculpture on the portal's capitals, with vegetal and floral themes, already announces a new aesthetics - the Gothic one - because its motifs, being already quite naturalistic, are closely bound to the basket. The slender columns that support them also bring us closer to this new moment in the history of art in the Middle Ages.
Although the layout of the façade tells us about the persistence of the Romanesque formulas, some of its compositional elements are clear testimonies of the introduction of new aesthetic models.
The main portal's tympanum, considered by Vergílio Correia (1888-1944) as the best specimen of its kind among coeval northern of Portugal churches, shows an elaborate multi-shaped hollow cross, richly decorated and remarkably carved.
We should also notice the three curious corbels that frame the portal, in which there are carved human faces that are rather hard to date.
The north and south lateral portals confirm the presence of the first rural Gothic style aesthetics. Both portals are carved into the thickness of the walls in which they were opened and feature a flat tympanum resting on corbels.
The north portal, which is more elaborate, comprises two archivolts surrounded by an external chequered arch, which also justifies the fact that it was sheltered by a porch-like structure, as suggested by the corbels that still currently exist in the middle of the façade.
On both elevations there are narrow crevices that, for being wider on their internal side, are characteristic of this type of constructions.
The corbels we find in Barrô show a great variety. On the north side they are richly decorated, while on the opposite side they are mostly plain.
Granite prevails inside the Church and the dimensions of the nave and chancel, particularly in terms of height, already announce the Gothic style. That fact is confirmed by the wide opening of the triumphal arch that, despite the aesthetic of its capitals, which is still very Romanesque, is already telling us about a different kind of liturgy.
Being slightly broken, the triumphal arch comprises two archivolts and is externally surrounded by an intertwined frieze. With a narrative nature, the capital found on the Gospel side shows us a hunting scene; its central figure is a man who, in addition to playing a hunting horn, is holding a spear in his right hand. The hunting horn was commonly used to communicate messages in times of danger.
On the right side there is a quadruped (perhaps bovine) and on the opposite side there is a character that seems to be armed with a sort of shield in the right hand and a club in the left hand. The topic of hunting, as an allegory of the struggle against evil, is also depicted on the opposite capital, where a boar is being grabbed by its paw and ear by two quadrupeds, perhaps two dogs.
The chancel is composed of three vaulted bays, defined by two transversal arches resting on columns addorsed to the wall. However, only the capitals on the central arch are ornamented, while the ones on the last arch are plain, something which may be explained due to the fact that this final bay is the result of an expansion of the apse to accommodate the ostentatious and spacious Baroque main altarpiece in a more balanced way.
We should notice the different size and colour of the ashlars from this final bay. So, it is in these two capitals from the chevet - decorated with bevelled vegetal motifs - that we find a great closeness to the Romanesque sculptural aesthetics of the ensemble that began developing itself in the Monastery of Paço de Sousa (Penafiel).
We may say that, after the Romanesque construction, it was during the Baroque period that the Church of Barrô underwent the most significant transformations. After its mainly stony decoration, there was a long period in which the horror vacui turned the whitewashed or plain walls into scenarios made of gilded and painted wood, according to the taste of a period when men sought to choreograph divinity.
In the chancel, the altarpiece drafted within the Johannine taste took up the entire chevet wall, moulding itself - in its scenic grammar - to the broken arch and giving rise a composition that stands in-between two styles.
The medieval Saint Mary was succeeded - already during the modern period - by the Virgin of the Assumption, which takes central stage on the main altarpiece and breathes the same style of the woodwork's language.
Still in the chancel, the large sculptural ensemble of the Calvary stands out, comprising a Crucified Christ, the Virgin and Saint John the Evangelist. Although it was transferred from an unknown location, this ensemble matches the Baroque spirit and the decorative language of the main altarpiece, so it was probably commissioned around the same time.
In the nave there are only two side altarpieces: one is dedicated to the Virgin of the Piety and the other symmetrical one, is currently dedicated to the Virgin and Child; in 1758, the Baby Jesus and the martyr Saint Sebastian were worshipped in this altarpiece.
Finally, we must not forget to mention the presence of numerous initials along the ashlars that embody the Church of Barrô.