"For four hundred and forty-one years from the foundation of the City, the Romans were satisfied with the use of such waters as they drew from the Tiber, from wells, or from springs. Esteem for springs still continues, and is observed with veneration. They are believed to bring healing to the sick, as, for example, the springs of the Camenae, of Apollo, and of Juturna."
Frontinus, The Aqueducts of Rome (I.4)
Now protectively sequestered behind a fence between the House of the Vestal Virgins and the three surviving columns of the Temple of Castor, a small shrine marks the spring that fed the Lacus Juturnae, a pool sacred to the nymph Juturna, beloved of Jupiter and the "glory of rivers, to my heart most dear" (Virgil, Aeneid, XII.142). It was here that Castor and Pollux (the Dioscuri) were said to have miraculously watered their horses after bringing news of victory at the Battle of Lake Regillus in 496 BC (Valerius Maximus, Memorable Doings and Sayings, I.8.1; Plutarch, Life of Aemilius Paulus, XXV.2; Life of Coriolanus, III.4).
"Of this extraordinary and wonderful appearance of these gods there are many monuments at Rome, not only the temple of Castor and Pollux which the city erected in the Forum at the place where their apparitions had been seen, and the adjacent fountain, which bears the names of these gods and is to this day regarded as holy" (Dionysius of Halicarnassus, Roman Antiquities, VI.13.4).
In this fragment from the Forma Urbis Romae (an incised marble map of Rome created by Septimius Severus sometime between AD 203–211), one can see the small lacus—and two pedestals in the basin, possibly for each of the Dioscuri. Curiously, the shrine itself is not depicted.
In 168 BC, Lucius Aemilius Paulus, in celebration of his victory over the Macedonian Greeks at the Battle of Pydna, adorned the basin with statues of the twins holding their horses, who again were thought to have appeared at the pool (Florus, Epitome, I.28.15; Valerius, I.8.1bc). Originally rectangular in shape, the basin was made square and a pedestal constructed in the middle to support the statue group. This may have been when the Temple of Castor was restored by Quintus Cecilius Mettelus in 117 BC and decorated with paintings and statues (Plutarch, Life of Pompey, II.4). Later, the size of the basin was reduced, possibly when Tiberius rebuilt the Temple in AD 6 (Suetonius, Life of Tiberius, XX; Dio, Roman History, LV.27.4). In the Augustan period, the sides of the basin were thickened and revetted with marble.
After the fire of AD 283, the shrine, itself, was rebuilt using the original architectural elements, including the architrave, which is inscribed IVTVRNAE S<ACRUM>. It sits on a high pediment with no approaching stairs and two slender Corinthian columns framing a shallow porch. The peculiar orientation, oblique to other nearby buildings, is due to its alignment with the Regia and the House of the Vestal Virgins, before it was rebuilt after the fire of AD 64.
Inside the apsidal cella was a cult statue of Juturna, the goddess of wells, springs, and fountains. The nymph, an ancient but lesser deity, and the waters over which she presided were thought to give nourishment and health, a etymology that Varro derives from juvare, "to help or assist" (On the Latin Language, V.71; also Statius, Silvae, IV.5.35–36; Propertius, Elegies, III.22; Servius, Commentary on the Aeneid of Virgil, XII.139, where her original spring at the foot of the Alban Hills was deemed so salubrious that its waters were brought to Rome for all sacrifices). The spring welling up in the Forum was one of its principle sources of water and, being close to the great temples, was used for religious sacrifice. A statue of Aesculapius found near the pool reinforces the notion that its waters were thought to have healthy properties.
In front of the shrine, now barely visible from a distance, is a marble well head with an inscription commemorating a first-century BC restoration by Marcus Barbatius Pollio, the curule aedile responsible for the maintenance of public buildings. It is obscured by a marble altar depicting an armed man and a woman with a lance. This may identify Juturna and her brother Turnus, king of the Rutuli, who in Virgil's Aeneid protected him as champion of the native Latins against the victorious Aeneas. Desired by Jupiter, Juturna was made the nymph of ponds and streams with "rule over all limpid things" in consolation for the loss of her virginity (XII.187–190).
Larunda (also Lara or Lala), another Naiad, warned of Jupiter's intentions and then betrayed the infidelity to Juno. For this inability to hold her tongue, Jupiter ripped it out and summoned Mercury to conduct the hapless girl to Hades. Equally smitten with her, she was raped and bore two children—the Lares, gods of the household and crossroads (Ovid, Fasti, II.585ff). This is not the find spot of the altar, however, and the relief may depict Mars and Venus.
An inscription from the early fourth-century AD on the base of a statue dedicated to Constantine by the curator aquarum suggests that the site by then had become headquarters for the Statio Aquarum (water board of Rome), the office having been transferred after the fire of AD 283 from the Campus Martius, where there is a Temple to Juturna (Servius, XII.139). Or it may be that the Lacus Juturnae simply was the cult site for dedications of the curatores.
The Juturnalia, was celebrated on January 11, when her temple in the Campus Martius had been dedicated, and all those who worked with water (the fontani, such as those who maintained aqueducts and fountains) honored the goddess.
Originally excavated only in 1900, when the Lacus Juturnae was discovered, and again in 1982, there was restoration of the area from 1953–1955, when travertine elements were added to the original brick and marble.
Immediately behind the shrine and half obscured by the ruined podium of the Temple of Castor is a modern building that protects a large fresco in the apse of the Oratory of Forty Martyrs. Dating from the eighth or ninth century, the wall painting, which is no longer open to the public, depicts the martyrdom of forty Christian soldiers who were exposed naked on a frozen lake near Sebastia, the capital of Armenia, in AD 320 during the persecutions of Licinius. Basil, bishop of Caesarea, provides the earliest account in a homily (XIX) delivered on their feast day.
The fragment from the marble map comes from the Stanford Digital Forma Urbis Romae Project and is identified as Stanford No.18a. The detail of the shrine was taken by Kalervo Koskimies shows the area when it still could be approached more closely.