License, verbatimCC0
Finnish National Gallery: CC0 1.0 Universal (the source record's image licence field reads 'CC0'). Free for any use, no permission needed.
Giovanni Battista Piranesi. View of the Walls that covered the slopes of Monte Celio, on which was Nero's Nymphaeum, and which adorned the Stadium of Domitian, 1756. Finnish National Gallery, Helsinki.