The temple of Apollo at Syracuse is located on the island of Ortygia and built from sandstone. It is one of the most ancient Doric temples in Sicily. It represents a transition between the archaic temples with a wooden structure, such a Pausanias describes the temple of Hera at Olympia, and those built completely from stone. It has a hexastyle front and a continuous colonnade enclosing the cella. At the back of the naos was a closed adyton, and contained the sacred image. The eastern end and entrance had a double set of columns acting as a portico, the columns spaced wider than on the flanks. The pioneering building was a defining step in the emergence of the peripteral Doric temple in Sicily. The temple's stylobate measures 55.36 x 21.47 metres, while the columns appear quite squat in compared with later Doric temples, such as that in Nemea or the temple of Zeus. On one of the steps of the east side is engraved inscription containing a dedication to Apollo.
The temple underwent several transformations: It was a Byzantine church, from which period the front steps and traces of a central door are preserved, and then an Islamic mosque during the Emirate of Sicily. Later it was restored to its previous purpose, then becoming the Norman Church of the Saviour, which was later incorporated into a 16th-century Spanish barracks and lastly into private houses.
Reference: Wikipedia, encyclopedia
SAINT-NON, Jean Claude Richard, abbé de. Voyage pittoresque ou description des Royaumes de Naples et de Sicile. Quatrième volume, contenant la description de la Sicile. Seconde Partie, Paris, 1786.
Mertens, Dieter; Schutzenberger, "Margareta. Città e monumenti dei Greci d'Occidente: dalla colonizzazione alla crisi di fine V secolo a.C.. Roma" L'Erma di Bretschneider, 2006.