Most visitors read the ancient glass in this house as colour. Scores of centuries-old panels are set into the first- and second-floor windows, and from across a room they are simply light — amber, cobalt, silver-yellow — moving across the oak as the sun goes round.

Stand close to the right window, though, and some of them turn out to be labelled. Painted around the rim of the roundel, in a careful seventeenth-century Latin hand, are names and dates. And three of those names belong to kings of Sweden.

CAROLUS IX — 1611

A bearded man in half-armour, shown from the chest up, with a heavy gold gorget and a small ruff at the throat. The lettering runs clockwise around him: CAROLUS · IX, and on the right-hand side a cross and the year 1611.

Charles IX of Sweden, father of the more famous man in the next window, died in 1611. The cross before the date is the old convention for a death year. The glass is, in other words, a memorial portrait.

GUSTAVUS ADOLPHUS — 1611 to 1632

The second roundel is a full standing figure in white and silver armour, a broad gold sash across the breastplate, standing on a band of deep red. The name arcs across the top; the two dates run down the right side, 1611 and 1632, with the same cross between them.

They are the years of his reign. Gustavus Adolphus took the Swedish throne on his father’s death in 1611 and was killed in November 1632 at the battle of Lützen, in the middle of the Thirty Years’ War, in which he had become the leading Protestant commander in Europe. His face is the one part of the panel that did not survive: the head is broken away and the gap carries a repair lead, so the king in the window is magnificently dressed and headless.

CAROLUS GUSTAVUS — 1622 to 1660

The third is the best preserved of the set: a young man with long hair falling over armour, a gold sash knotted at the waist, his face intact and slightly wary. The inscription gives both a birth year and a death year — 1622 and 1660.

That is Charles X Gustav, Gustavus Adolphus’s nephew, who succeeded Queen Christina in 1654 and died six years later. Three panels, three men, and between them the whole arc of Sweden’s great-power century — the grandfather, the warrior king, and the nephew who inherited what the war had won.

How did Swedish kings end up on Twenty-Second Street?

Honestly: nobody wrote it down. What the house’s records do trace is the route the ancient glass took as a whole. For roughly six hundred years Salisbury Cathedral served as a repository for shards of old European glass — panels rescued from churches and houses broken up in the religious wars. In the late 1800s the London dealer Grosvenor Thomas acquired the collection. Charles Duveen — Charles of London — brought him to New York, and in 1913 the shards went on display at Duveen’s Fifth Avenue showroom, where Vanderbilt, Hearst, Guggenheim, Getty and Charles S. Pillsbury bought them up.

Some panels in this house carry the crest of Friedrich Magnus zu Salm, a general of the Dutch States Army in exactly this period, who gave a series of windows to the Cathedral of St Michael in Brussels; they were taken down for safekeeping during the French Revolution and eventually made their way to Salisbury. Whether the Swedish roundels travelled in that same crate, we do not know. The panels are their own documentation. Two earlier pieces follow the paper trail further: the Costessey collection and where the mansion’s ancient glass came from.

What else is hiding in the windows

Once you start reading rather than looking, the windows get busy. One panel is an Annunciation — the Archangel Gabriel appearing to the Virgin Mary, a lily between them. The colours are chemistry as much as art: the yellows are silver oxide, the blues cobalt, and the black outlines are iron oxide painted on like enamel and fired until they fused into the glass. That is why six centuries of weather have not washed the faces off.

Another shows King Ahasuerus and Haman at the Feast of Esther — the moment Esther names the plot against her people, and Haman’s fate turns. It is Flemish painted glass of 1660, and it copies a Dutch painting which was itself a copy of a Rembrandt. A copy of a copy, four hundred years old, glowing in a Minneapolis window. There is a whole essay in the fact that nobody in 1660 thought that was a scandal.

And the empty spaces

Look along a run of windows and you will find gaps — plain quarries where a panel clearly used to sit. From 1939 to 1969 the mansion was a Lutheran seminary, and the priests judged certain of the images too worldly for the young men studying here. Those panels were quietly taken out. Where they went is one of the questions this house has never answered.

The rest of the collection is set out on the splendors, alongside the Rotherwas oak, the Tudor plaster ceilings and the two great imported fireplaces; the dealers who assembled it are on the Duveen brothers. If it is the heraldry you want rather than the portraits, we went through the coats of arms carved into the house last week.

Come and read them yourself

The lettering is small and the light is best in the middle of the day. Guided tours of the mansion run year round — see experiences and tours, and plan your visit for hours and directions. Bring your reading glasses; the kings are worth the squint.

And if the Swedish thread interests you, Minneapolis has form: the American Swedish Institute keeps its own mansion a few blocks south of here, in the Turnblad house on Park Avenue. The Pillsbury Mansion is listed on the National Register of Historic Places; for the wider story of the city that paid for it, the Mill City Museum is the place to start.

Keep reading: Why Did the Pillsbury Mansion Sit Unbuilt for Four Years?