Is "The Dioscuri on Monte Cavallo; verso: Study of a Spiral Staircase" in the public domain?

Yes, The Dioscuri on Monte Cavallo; verso: Study of a Spiral Staircase is in the public domain and available for free download under CC0 license.

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The Dioscuri on Monte Cavallo; verso: Study of a Spiral Staircase

This artwork was created ca. 1533.

Maarten van Heemskerck, ca. 1533