It was built at the end of 2nd century AD in front of the temple of Apollo and large stone blocks and marble slabs were used for construction. It had originally 2 floors but today just back and side walls are standing. This monumental fountain known as Nymphaeum and it conveyed water to the houses trough a special distribution system. Nymphs used to live in the forests or in water and did not show themselves to humans. 

When they became angry with humans they used to cut off their water supply and cause droughts. So nymphaeum was built to show gratitude and to gain favor of the nymphs.