You are looking at one of Rome's earliest colossal temples. It was originally dedicated on December 17, 497 BCE on the site of a very old shrine in honor of the god Saturn. December 17 was the feast day of Saturn, and marked the beginning of the festival of the Saturnalia. The temple was rebuilt in 42 BCE by L. Munatius Plancus; the existing podium derives from this restoration. After serious damage by a fire, it was restored again in the last third of the fourth century CE.
Beneath the unusually high stairs and podium was the state treasury (aerarium); its entrance can be seen in the eastern base of the temple in this reconstruction. The present remains of the temple (seen at the right in this photo) continue to be impressive, especially the columns that tower over observers.
The temple sits awkwardly located on the Vicus Jugarius between the Basilica Julia, directly to the east, and the Clivus Capitolinus, the slope of which rises directly adjacent to its western side. This accounts to a certain extent for the unusual design of the front steps.
Reconstruction images courtesy of UCLA's Digital Roman Forum.