Forum Romanum, Rome. South-western corner of the Basilica Julia to the three remaining columns of the Temple of Castor and Pollux.

The Basilica Julia (Italian: Basilica Giulia) was a structure that once stood in the Roman Forum. It was a large, ornate, public building used for meetings and other official business during the early Roman Empire. Its ruins have been excavated. What is left from its classical period are mostly foundations, floors, a small back corner wall with a few arches that are part of both the original building and later Imperial reconstructions and a single column from its first building phase.

The Basilica Julia was built on the site of the earlier Basilica Sempronia (170 BC) along the south side of the Forum, opposite the Basilica Aemilia. It was initially dedicated in 46 BC by Julius Caesar, with building costs paid from the spoils of the Gallic War, and was completed by Augustus, who named the building after his adoptive father. The building burned shortly after its completion, but was repaired and rededicated in 12 AD. The Basilica was again reconstructed by the Emperor Diocletian after the fire of 283 AD.
The Basilica Julia was partially destroyed in 410 AD. when the Visigoths sacked Rome and the site slowly fell into ruin over the centuries. Part of the remains of the basilica was converted into a church in the 7th or 8th century. The building consists now only of a rectangular area, levelled off and raised about one metre above ground level, with jumbled blocks of stone lying within its area. A row of marble steps runs full length along the side of the basilica facing the Via Sacra, and there is also access from a taller flight of steps (the ground being lower here) at the end of the basilica facing the Temple of Castor and Pollux.

It was the favorite meeting place of the Roman people. The Basilica housed the civil law courts and tabernae (shops), and provided space for government offices and banking. In the 1st century, it also was used for sessions of the Centumviri (Court of the Hundred), who presided over matters of inheritance.

The Temple of Castor and Pollux (Italian: Tempio dei Dioscuri) is an ancient edifice in the Roman Forum, Rome, central Italy. It was originally built in gratitude for victory at the Battle of Lake Regillus (495 BC.). Castor and Pollux (Greek Polydeuces) were the Dioscuri, the "twins" of Gemini, the twin sons of Zeus (Jupiter) and Leda. Their cult came to Rome from Greece via Magna Graecia and the Greek culture of Southern Italy.
The octastyle temple was peripteral, with eight Corinthian columns at the short sides and eleven on the long sides. There was a single cella paved with mosaics. The podium measures 32 m × 49.5 m (105 ft × 162 ft) and 7 m (23 ft) in height. The building was constructed in opus caementicium and originally covered with slabs of tuff which were later removed. The temple was probably already falling apart in the fourth century, when a wall in front of the Lacus Juturnae was erected from reused material. Nothing is known of its subsequent history, except that in the 15th century, only three columns of its original structure were still standing. The street running by the building was called via Trium Columnarum.
The last king of Rome, Lucius Tarquinius Superbus, and his allies, the Latins, waged war on the infant Roman Republic. Before the battle, the Roman dictator Aulus Postumius Albus Regillensis vowed to build a temple to the Dioscuri if Rome were victorious.
According to legend Castor and Pollux appeared on the battlefield as two able horsemen in aid of the Romans. And, after the battle had been won they again appeared on 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.
In Republican times the temple served as a meeting place for the Roman Senate, and from the middle of the 2nd century BC the front of the podium served as a speaker's platform. During the imperial period the temple housed the office for weights and measures, and was a depository for the State treasury.

more on https://en.wikipedia.org/wiki/Basilica_Julia , https://en.wikipedia.org/wiki/Temple_of_Castor_and_Pollux , https://en.wikipedia.org/wiki/Roman_Forum , https://de.wikipedia.org/wiki/Datei:Map_of_downtown_Rome_during_the_Roman_Empire_large.png http://dlib.etc.ucla.edu/projects/Forum/reconstructions/ForumRomanum_1