In today’s Latvia, only a few bay windows older than the rich historical quotes of the 19th century Historicist period are on view in their original locations. A bay window built in the mid-17th century has survived in the northwest corner of Riga Castle; this is the only such ancient structure in Latvia whose artistic quality permits comparisons to other Mannerist and Baroque examples of Northern Europe. Especially significant in Latvia’s history of architecture and art are the decorative reliefs on the bay window façades. This article aims to bring together the information we have so far and include changes resulting from the latest studies. This means giving a precise picture of how much and what exactly has been preserved from the original bay window construction and analyse its architectonic and artistic significance in the context of Riga’s 17th century architecture, while adding new facts to the known construction history. The walls of the Riga Castle bay window are made of a stone framework with decoratively treated slabs filling the space between the uprights and profiled horizontal cornices beneath the window openings. Each storey has a separate small, octagonal premise with doors leading to the rooms inside the block. The initial openings of the bay window were twice as high as those visible now. The stone walls were doubled inside with a half-timbered construction. Historians have researched the Riga Castle bay window several times. However, these studies are scattered over a prolonged period and largely mutually unrelated. Art historians are interested in the origins of the bay window’s façade reliefs – expressive Baroque artefacts. In the second half of the 16th century, both blocks of the forecastle’s northwest part were reconstructed for the needs of the Polish local potentate’s institutions and apartment. In the second quarter of the 17th century, the Swedes also arranged their headquarters in the same forecastle blocks. However, furnishing works of the residence dragged on because of simultaneous large-scale improvements to the fortification system. The Swedish governor’s general residence was completed around the mid-17th century. Portals marked several entrances, and the bay window was an expressive element of the façade décor. As seen from year numbers on two reliefs, elements of the bay window were completed in 1649; it was likely built into the corner of the forecastle blocks about the same time. This period coincides with the reign of Queen Christina (1626–1689), daughter of Gustav II Adolf (1594–1632). The Riga Castle bay window has two storeys, a hexagonal form and a Baroque, tower-shaped roof. Its façades consist of five planes composed of vertical elements and horizontal dividing cornices with 20 bands of decorative reliefs in total, initially made of Gotland sandstone. The message of the reliefs is arranged on two levels. Now the bay window contains copies of reliefs made of Saaremaa dolomite in the 1960s. An established assumption attributes the authorship of the bay window reliefs to the stucco master from Mecklenburg Daniel Anckermann (1590–1665). He could have worked in Riga in the 1630s. In 1647, he came to Riga but no information has survived on potential commissions. Also, no written evidence confirms Anckermann’s return to Riga in 1649. Assuming that the bay window and reliefs were made in 1649, a more plausible hypothesis is that local masters crafted the reliefs, using Anckermann’s design. Anckermann’s authorship is credible because of his contacts with the De la Gardie family. Precisely in 1649, Magnus De la Gardie became the Governor General of Swedish Livonia and carried out reconstruction works at Riga Castle. De la Gardie probably commissioned the bay window but its designer remains unknown so far. In August 1641, Anckermann worked in Sweden, arranging the interior of Makalös Palace. A Mannerist mask from Makalös is visually similar to masks in the reliefs of the Riga Castle bay window. Possibly these examples influenced Magnus De la Gardie’s commission of the Riga reliefs. Each of the bay window reliefs is different. Using the popular grotesque elements of late Mannerism, the reliefs depict parts of the coat of arms of Sweden as well as those of the House of Vasa. Figures of a soldier and a woman have been added, using auricular ornament as well as C and S-shaped ornamental motifs. Most of the reliefs on view allow us to conclude that a unified artistic idea was behind the bay window façades. Considering the political context and facial likenesses, it would be safe to presume that portraits included in the reliefs depict representatives of the House of Vasa, i.e. the King of Sweden Gustav II Adolf and his daughter Christina who subsequently ruled from 1644 to 1654. A portrait of Gustav II Adolf by Jacob Heinrich Elbfas (1600–1664) was the probable source of the likeness. The image of Christina could have been derived from her portrait dated 1640 also by Elbfas. The year 1874 is particularly remarkable in the history of the Riga Castle bay window; capital repairs and restoration were carried out then and these works are among the oldest attempts at restoring a historical building in the history of Latvia’s monument protection. Today different images can be seen in the reliefs. Only a small part of the original 17th century constructions have survived to the present day – the lower consoles and the stone framework of the second-storey window openings. In 1874, the zone of the lower-storey window openings was completely reconstructed, using artificial stone of lime-cement mortar while the reliefs themselves were carved from Saaremaa (Estonia) dolomite in 1965. This is sculptor Marija Ehelaide’s improvisation on the theme of the bay window’s original reliefs. Comparative analysis of the photographed reliefs causes reasonable doubt whether everything possible and necessary for the creation of flawless copies had been done in the 1960s. Unfortunately, the further destiny of the originals remains unknown. The stone constructions of the bay window were carefully examined in every detail during the last restoration in 2013. Various changes have affected the façade and roof of the bay window but overall it has been restored closely to its initial form. Regardless of the details transformed over time, they give an idea of the artistic expression of the original reliefs and the programmatic message of the bay window’s décor. Even in the form of copies, this clearly demonstrates the artistic and architectural tendencies of a particular epoch, remaining among the most significant examples of 17th century Northern European Mannerist sculpture in Latvia.