Above the west door, carved into the stone, an inscription gives a date and a name. The date is 1028. The name is Christopher, protospatharios and katepano of Longobardia, which is to say a Byzantine official with a long title and a posting in southern Italy. He built the church with his wife, his son, and his two daughters. Most founders of medieval churches lie buried in the narthex, the entrance hall where visitors must pass them on the way to worship. Christopher chose differently. His tomb is set into a niche in the north wall of the nave itself, an arcosolium tucked close to the altar. The choice may explain a peculiarity of the painted dome. Where most Byzantine churches show Christ Pantocrator gazing down from the apex, here the dome shows the Ascension. Art historians read it as a funeral commission, a man preparing the place where he would wait for resurrection.

The architecture is what scholars call a cross-in-square, a plan that became the standard form for middle Byzantine churches across the empire. Four arms reach out from a central square, each crowned with a saddleback roof and a triangular pediment. Domical vaults fill the corners. The whole composition is built in red brick, decorated with recessed arches and dentil courses, the kind of brickwork that catches afternoon light and seems to vibrate against the city's pale modern facades. It is small. You can walk around the outside in a couple of minutes. But the proportions are so carefully judged that the building reads as monumental, a complete idea executed at intimate scale, the way a well-cut gem can outweigh a boulder.

Inside, fragments of an eleventh-century fresco cycle still cling to the plaster. On the south wall of the bema, the apostles receive the bread of the Last Supper. On the north wall, mostly ruined now, they would have received the wine. The arrangement encloses the altar itself, so that the priest celebrating the liturgy stood at the visual center of the painted scene. The earliest known depiction of the Last Supper in the sanctuary of a Byzantine church is right here, drawn around the spot where the eucharist was actually performed. In the narthex, a Last Judgment unfolds across the walls, with Christ enthroned above the inner door. The figures are flat, heavy-lined, full of shading and color, and after a thousand years they still hold the eye.

When the Ottomans took Thessaloniki in 1430, the Panagia Chalkeon became a mosque. It served the city's Muslim community for nearly five centuries, an arc of history almost as long as its time as a church before that. The Ottoman occupation ended in 1912. After the Chalkidiki earthquakes of 1932 cracked the structure, restorers spent years putting it back together, and in the twentieth century it was reconsecrated. UNESCO listed it in 1988 as one of fifteen Paleochristian and Byzantine monuments of Thessaloniki. The coppersmiths are long gone from the streets outside. The Virgin they dedicated their church to remains, looking out over a quarter that no longer remembers how to make a copper pot but still knows the building that anchors it.