I found the Tower of Mercury open only once in all the times I've visited
Pompeii. I took this photo
looking south from the top of the tower. As illustrated here,
practically all roofs of houses in Pompeii collapsed when ashes accumulated
on them during the volcanic eruption.
On a clear day, the view from the top of the tower is incredible. In the distance are the Lattari Mountains which form the Sorrento Peninsula on the southeastern side of the Bay of Naples.