The construction of the church of St. James probably began around 1370. The main part of the work, that is the nave and the ground floor of the tower with chapels, was probably completed in 1380. In the 16th century vaults were built, and in 1596 the tower was raised to 7 storeys.
In the 17th century, due to the impoverishment of the parish, the interior of the church and its walls remained neglected. It was not until 1721 that Piotr Olchowski from Reszel reconstructed the two falling into ruin chapels. The church was severely affected by the quartering of Napoleonic troops in 1807. In 1819, the vault over the organ gallery collapsed, and in 1864 the entire building was in danger of collapsing and had to be closed. The church was put into use after a general renovation carried out in the years 1866-1868, but the work on the interior lasted a dozen or so years longer. During World War II, the church was saved from destruction by Fr. Jan Hanowski, who managed to get the Russians to save the church.
The church was erected just above the slope, near the north-eastern corner of the city walls. It was built of bricks on a stone foundation, as a three-aisle, six-bayhall, without a separate chancel with a massive and high tower on the west side flanked by a pair of chapels. The nave of the church was 58 x 24 meters, and the tower was 70 meters high. The massive, monumental building originally had no annexes, even the sacristy was placed inside the southern aisle. The eastern façade of the nave was decorated with a Gothic gable decorated with pinnacles and blendes, above which there were round openings protruding above the roof (a motif also found in the Kwidzyn cathedral and the Olsztyn castle). Its height reached about 38 meters. The nave was enlivened by the rhythm of buttresses and pointed windows with traceries.
The tower has seven storeys separated by horizontal, plastered stripes, which up to the third floor are decorated with glazed tracery. All its walls are decorated with two-arch blendes. The highest storey is topped with an arcaded frieze and cornice. In the center of the facade there is the main entrance to the church, a strongly moulded, pointed portal.
The central aisle was covered with a net vault and diamond vault was placed in the side aisles, based on five pairs of smooth, massive, octagonal pillars supporting high, pointed, moulded arcades. The vault corbels were designed in the form of polychrome, bearded male heads, made of terracotta.
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Kościoły i kaplice archidiecezji warmińskiej, tom 1, red. B.Magdziarz, Olsztyn 1999.
Lesiński A., Olsztyńska bazylika katedralna św. Jakuba na przełomie wieków, Olsztyn 2009.
Rzempołuch A., Przewodnik po zabytkach sztuki dawnych Prus Wschodnich, Olsztyn 1992.
Website katedra.olsztyn.pl, Rys historyczny.