Bartolomeo Vivarini
Altar of Our Lady of Mercy: Detail, St. Anne and St. Joachim at the Golden Gate

As in a predella panel of a few decades later, an angel encourages the couple's embrace. The Golden Gate is represented both by a painted arch and by the sculptural arch that encloses the painting.

This is on the left side of the altar. The larger central painting is of Our Lady of Mercy, and the right side has the Birth of Mary.

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Photographed at the church by Richard Stracke, shared under Attribution-NonCommercial-ShareAlike license.