According to legend, Castor and Pollux appeared on the battlefield as two able horsemen in aid of the Republic. After the battle had been won, they again appeared in the Forum in Rome, watering their horses at the Spring of Juturna, thereby announcing the victory. The temple stands on the supposed spot of their appearance. It is situated on the eastern flank of the Vicus Tuscus, at the intersection with Via Sacra.

In antiquity, the Temple of Castor and Pollux was often referred to as aedes Castoris, briefly as the Temple of Castor or the Temple of the Castores. This shorthand reflects common naming conventions in Roman culture, where long formal names were frequently abbreviated in casual or practical usage.

Commemorating Republican Rome's victory at Lake Regillus, a large cavalry parade was held annually on July 15, featuring as many as 5,000 young men carrying shields and spears. Two young men, riding white horses, led the parade and represented Castor and Pollux.

circa 500 BCE-

Roman Republic: First Temple
After his ovethrow in 509 BCE the last king of Rome, Lucius Tarquinius Superbus, and his allies, the Latins, waged war on the infant Roman Republic in circa 496 BCE. Before the Battle of Lake Regillus, the Roman dictator Aulus Postumius Albus Regillensis vowed to build a temple to the Dioscuri (Castor and Pollux) if the Republic were victorious.

After the Romans decisively defeated Tarquinius' forces, the construction of the temple began in or around 484 BCE. According to some accounts, the date of the temple's dedication was the 15th of July, known as the Ides of July, and the project was carried out under the auspices of one of Postumius' sons. This son, who held the position of duumvir, played a significant role in overseeing the dedication of the temple.

It was a large structure for its time and served as a significant place of political and social importance in early Roman society. This temple was built in a Tuscan style, reflecting early Roman temple architecture, with wooden columns and entablatures. The architectural simplicity of the period is evident in the use of wide intercolumniations and low ceilings, which were typical of Roman temples before the widespread use of stone columns. During the Republican period, the temple served as the primary meeting place for the Roman Senate, and from the middle of the 2nd century (circa 150 BCE), the front of the podium served as a speaker's platform.

Roman Republic: Second Temple
The archaic temple, built during the early years of Republic, had deteriorated and was completely reconstructed and enlarged in 117 BCE by Lucius Caecilius Metellus Dalmaticus, Roman politician and general, after his victory over the Dalmatians. This reconstruction was largely in tufa (a local stone) and stucco. Despite its political importance, the structure was considered poorly built and required repairs less than fifty years later. This temple served as a focal point for political activity and was used for Senate sessions and other important civic functions. However, it was criticized for being poorly built, leading to the need for repairs by Verres in the 1st century BCE. Gaius Verres restored this second temple in 73 BCE.

In 58 BCE, Cicero mentions in some of his orations, that the grand stairs in front of the temple were removed or torn down by his opponent P. Clodius. Around the same time the temple is also known to have been used as a bank for private depositors.

Roman Imperial Period: Third Temple
During the imperial period or the Roman Empire period, the temple housed the office for weights and measures and was a depository for the state treasury. Chambers located between the foundation piers of the temple were used to conduct this business.

In 14 BCE, a fire destroyed the temple, and was extensively rebuilt by emperor Tiberius. The new temple was dedicated in 6 CE. The remains visible today are from the temple rebuilt by emperor Tiberius, except the podium, which dates to the time of Metellus.

Around the same time, in conjunction with the rebuilding, the cult became associated with the imperial family. Initially, the twins were identified with Augustus's intended heirs, Gaius and Lucius Caesar. After their premature deaths, the association passed to Tiberius and his brother Drusus.

Edward Gibbon noted that the temple served as a secret meeting place for the Roman Senate. According to Gibbon, the Senate was roused to rebellion against Emperor Maximinus Thrax in favor of Emperor Gordian I and his son Gordian II at the Temple of Castor and Pollux in 237 CE.

If still in use by the 4th century CE, the temple would have been closed, along with that of Temple of Saturn, during the persecution of pagans in the late Roman Empire. By the 15th century CE, only three columns of its original structure were still standing. The street running by the building was called Via Trium Columnarum.

In 1760, repairs were made to the remaining columns to prevent collapse. Today, the podium survives without its facing, along with the three columns and a piece of the entablature, which are among the most famous features in the Forum.

circa 1200 BCE

The octastyle temple was peripteral, with eight Corinthian columns on the short sides and eleven on the long sides. All that now remains are three graceful Corinthian columns on the east side, still surmounted by an entablature with a plain frieze and modillion cornice. The Temple of Castor and Pollux uses the Corinthian order, which is distinguished by its ornate and elaborate design, notably its acanthus leaf capitals. The column proportions and the decorative richness highlight its adaptation for grand and ceremonial use, particularly in temples and public buildings of the Roman era. The column capitals, with their intricate detailing, are a defining feature of this style, contributing to the temple's visual impact.

The temple featured a single cella paved with mosaics. The podium measures 32 meters by 49.5 meters (105 by 162 feet) and is 7 meters (23 feet) in height (approx. 2 meters lower than that of Temple of Saturn).

The building was constructed in opus caementicium and originally covered with slabs of tuff, which were later removed. Ancient sources indicate the temple had a single central stairway to access the podium, but excavations have revealed two side stairs as well. The two side stairs may have connected to a central larger stair case.

The third temple of Dioscuri built by Tiberius in the Roman Forum was a monumental reconstruction that emphasized both stability and grandeur. One of the most notable features was its foundation and podium. The original podium had become structurally unreliable, prompting a complete overhaul. A new foundation made of solid masonry (inspect) was constructed to support the expanded structure, ensuring its longevity. This foundation was surrounded by a sturdier masonry platform, which elevated the temple and added to its impressive scale. The use of solid masonry ensured that the temple would stand the test of time, particularly given the added weight and size of the new superstructure.

Moving upward, the columns of the third temple of Castor and Pollux were made from marble, a choice that marked a shift toward more luxurious materials compared to the previous iterations of the temple. The use of Corinthian columns was a defining architectural feature, embodying the Roman preference for grandeur and elaborate decoration. Corinthian capitals, rich with acanthus leaf motifs, added a sense of opulence and grandeur to the structure. These columns were placed strategically to support the temple’s roof, which was constructed with wooden trusses. This technique eliminated the need for interior columns, allowing for a more open and spacious interior. The decision to use wooden trusses for the roof not only provided structural stability but also facilitated easier construction compared to heavier stone materials.

The cella, or inner chamber of the temple, was expanded to accommodate the temple’s growing significance as both a religious site and a civic building. The walls of the cella were built with tufa blocks, a lightweight volcanic rock that provided stability and insulation. The exterior of these walls was coated with stucco, a technique that allowed for a smoother finish and added a decorative layer to the building’s surface. The use of stucco was a common Roman method of enhancing the aesthetic appeal of large structures, creating an elegant contrast with the more utilitarian building materials like tufa.

One of the most practical features of the temple built by Tiberius was its speaker’s platform. This raised area, originally part of the temple’s design, became even more important as a space for public addresses and senatorial meetings. The temple’s function as a political center was reinforced by the expansion of this platform, which allowed it to accommodate more people. The platform was seamlessly integrated into the temple’s design, elevated by the increased height of the podium and accessed by a series of steps. These steps were carefully crafted to fit the new height of the podium, ensuring that visitors could easily ascend to the temple’s entrance.

The temple’s roof and entablature were designed to complete the grandeur of the structure. The roof was likely covered with tiles, while the ceiling featured paneling, which contributed to the overall refinement of the interior space. Cicero humorously mentioned these paneling details, highlighting their intricate design. The entablature, consisting of travertine, was another striking feature. The use of peperino, a volcanic stone, added a contrasting texture to the entablature and other decorative elements, enhancing the temple’s aesthetic appeal. The architrave, a horizontal beam supporting the columns, was adorned with moldings and fasciae, adding subtle decoration to the temple’s facade. The frieze and cornice, possibly decorated with stucco reliefs, further emphasized the temple's elegance and attention to detail.