Of the temples in Agrigento's Valle dei Templi, Concordia is the one that looks, at a glance, almost exactly as it did when it was finished around 440–430 BC. Six columns stand at each short end, thirteen along each long side, thirty-four in total, each carved with twenty shallow flutes and a subtle swelling at the middle (entasis) that keeps the straight stone looking alive rather than rigid. Both pediments and most of the entablature survive largely intact, a level of completeness matched by almost nothing else from the ancient Greek world outside a handful of sites in Greece itself.
Unlike the Parthenon, its far more famous cousin in Athens, Concordia has no elaborate sculpted frieze or figures on its metopes. That plainness may reflect a distinct regional taste, shaped as much by nearby Carthaginian and Egyptian influence as by mainland Greece, or it may simply be a practical choice. Either way, it leaves the temple's proportions and craftsmanship to carry the whole effect, and they do.
Photo via Wikimedia Commons (CC BY-SA 4.0)
The reason Concordia survives so completely, while its neighbours were reduced to scattered blocks, comes down to one decision. Around 597 AD, the bishop Gregorius converted the temple into a Christian basilica, consecrating it to Saints Peter and Paul. Rather than demolishing the pagan structure, his workers cut twelve arches through the walls of the cella and reused the building whole, arches still visible today, along with tombs cut into the floor from this period. According to local tradition, Gregorius first had to expel two pagan spirits from the building, named Eber and Raps, a story colourful enough that the church that replaced the temple became informally known as "St. Gregory of the Turnips," after a folk mistranslation of Raps' name.
The temple stayed a working church for well over a thousand years. It was only in 1785, under the Prince of Torremuzza, that the Christian-era additions were dismantled and the building restored to something close to its ancient Greek form, the version you see today. Its name, incidentally, has nothing to do with its original dedication (unknown, possibly Castor and Pollux): "Concordia" comes from an unrelated Latin inscription the 16th-century historian Fazello happened to find nearby, and the label simply stuck.