As a member of the Decapolis, or the ten Roman cities of the Middle East, Amman was an important site for the construction of Roman infrastructure. One such example is the Nymphaeum, a now largely destroyed construction that would have been dedicated to nymphs and would have, practically, functioned as a fountain and possibly a bath. Although much of the structure in central Amman is now destroyed, it is evident from what remains that it would have been quite large and solidly built, a tribute to the importance of Philadelphia. What's more, the presence of roughly hewn block construction around it indicates that later invaders and occupiers of the city must have identified its importance as part of the site's infrastructure, and sought to protect it during times of instability.
Located in the heart of downtown, the Nymphaeum of Philadelphia dates back to 191 AD. It was once twice its current size and decorated with statues and mosaics, and had a large pool fed by the waters of a stream now buried under the modern streets. The side facing the main street looks more like a castle with its imposing round towers (was it perhaps fortified at a later date?). The Nymphaeum now lies in ruins among modern buildings of Amman and had been closed for reconstruction for sometime. Beautifully carved blocks of stone are piled up on the site waiting for their turn in the reconstruction. Although the work had not yet been completed when I visited Amman in August 2008, the site had been left open for anyone to walk in and inspect. My host in Amman and I had the pleasure of being the only visitors!
Update: upon my second visit in Dec 2010/Jan 2011, no additional reconstruction work seemed to have been done, but the site was again open for anyone to walk inside.
At a busy traffic intersection in Downtown Amman are the ruins of a Nymphaeum. The Temple itself is fenced. It is located a few blocks from the Roman Amphitheatre, in the direction of Grand Hussieni Mosque.
This huge fountain was built in 191 AD. It was the chief fountain for the ancient city of Philadelphia.
Close to the theatre, you can see as well the remaining of a huge roman fountain dedicated to the Nymphs.
As you can see on the picture, they are currently renovating it.