Here's the image by Piranesi portraying the aqueduct in Roman times:
Here is Piranesi portraying it somewhat in ruins but still functioning, in his 1762 Il Campo Marzio. A large opening was cut in the aqueduct to fill up a large basin, which was used for washing clothes.
Here is a painting from the early 19th century showing the elevated level of the aqueduct -- higher than today, and the basin in use. In the painting, you can see in the background the roadway -- Via Nazareno -- above the arch. The engraved Latin inscription is today barely visible.
And here are images of it today, May 9, 2014.