Nymphaeum (Olympia) (Latin, Ancient Greek: νυμφαῖον), etymologically "home of the nymphs" or water goddesses, at ancient Olympia was the official name of a water-distribution structure constructed in the mid-2nd century at that site to provide water to the masses who attended the Olympic Games in July and August.

Nymphaeum was the general name throughout the Mediterranean for an ornate structure that terminated an aqueduct bringing water from distant elevated terrain, say a stream or copious springs.

It received water from the aqueduct into a cistern and released it by stages into a system of open and closed channels leading around the site.

Prior to then the more permanent population of athletes, trainers, and administrators relied on wells or short conduits to the Kladeos River, while the spectators suffered greatly, with only the water they could carry in.

In mid-century Herodes Atticus, a wealthy savant, engineer, and friend, teacher, and confidant of emperors, was invited to attend the games with his wife Regilla, who was made an honorary priestess of Demeter to get around the exclusion of women.

By the next Olympiad, a first-rate water distribution system, which came to be known as the Nymphaeum of Herodes Atticus, had been constructed.

The engineering team had to locate a good source of fresh water and build an aqueduct from it, tunneling through the hill.

As it turned out, the source was very likely part of the municipal water supply of ancient Greek Pisa.

The Nymphaeum and its entire water supply system are historical developments of Roman Olympia; that is, of the imperial period during which the Romans took a deep interest in the Olympic Games, contributing funds to Olympia, helping to manage the site, competing in its games, and contributing to the new Greco-Roman culture.

[2] Finally defeating the last contenders of the long Roman civil war, Octavius Caesar implemented the plan he had made with his adopted father, Julius.

[3] The lower Kladeos could not be used because all rivers next to settlements received the effluent of sewer ditches, mainly latrines.

[note 2] On the south side, the swifter and more copious Alpheios was of little help because the water, flowing through limestone its whole distance, was too hard (high in dissolved carbonates) to drink.

It was probably true that some people, such as the athletes, trainers and managers, as well as important visitors, had no problem obtaining water.

The masses that arrived in July and August, the hottest months of the year, unrelieved by rain, apparently suffered the most.

Infectious diseases were rampant, which the citizenry blamed on lack of water (being unfamiliar with microbes).

The Romans built chutes, or aqueducts, that descended at a low gradient, crossing valleys on bridges and going through hills in tunnels.

At the terminus was an elaborate distribution structure, called in the 2nd century a nymphaeum, "home of the nymphs," or water goddesses.

It is in the building of these systems that Herodes Atticus had become in essence a civil engineer with expertise in water supply.

It was the duty of wealthy men to manage projects such as these, as it had been under the Republic, at their own expense, or assisted by empire funds, although they could levy taxes to cover it (not a popular method).

"[9] The terrain map shows Erymanthos as a massif in the vicinity of Pothos (37°42′09″N 21°41′14″E / 37.70253°N 21.68732°E / 37.70253; 21.68732 and Lalas (37°42′37″N 21°43′12″E / 37.71020°N 21.72002°E / 37.71020; 21.72002), with a long ridge extending to the SW, of which Kronion is the very last hill.

As an established archaeologist would have been familiar with both the hydrology and terrain maps, an explanation might be sought in the original date of his comment, which was perhaps before discovery and excavation of the remaining aqueduct.

The high end of the aqueduct at about 55 m is matched by the elevation of the river at Koskinas 2 km north of Olympia.

The only other remnant was a projection above the surface on a hilltop in the village of Miraka, now in downtown Pisa, reported about the time of the excavation of Olympia.

The elevation is about 108 m (354 ft), but only ephemeral streams are in the vicinity, not much good for permanent water sources.

[10]: 252  The imbalance was probably not much different in classical times; i.e., the water was to be found in the mountains, which is where Herodes Atticus' engineers would have looked for it, in the "hills of Linaria and Muria.

The mountain stream descends as a pebble-bottom ditch choked with vegetation from springs and waterfalls of the upper col until it reaches Tripotama as a good-sized, fast-flowing shallow river.

Starting in 2013, a new water treatment plant on the Elis side of the middle Erymanthos river began delivering (via gravity-flow underground channels) a fixed rate of 0.6 cubic meters per second of drinking water on a fixed monthly schedule to all the communities downstream in the Alfeios system as far as Pyrgos; i.e., all north and central Elis.

All the hydrologic circumstances together offer a credible view of Herodes Atticus' engineering plan and account for its success, although little of it can as yet be proved by regional archaeology.