As you enter Pompeii this will be one of the first ruined buildings you see on the left. Various artifacts from several different cultures found at this site suggest there was a vigorous cult of Apollo in Pompeii. The basic floor plan of this building dates to a time before the Romans controled the area. (about 2nd Cent. B.C.) It showed frequent modifications and was under renovation (probably from an earthquake in 62 AD) at the time of its final destruction in 79 AD.
There were 48 columns around a peristyle (covered walkway around the outer edge of a courtyard), the ruins of which you can see in the pictures below. The actual temple is the raised area in the center.
The bronze figure of Apollo to the right of the picture is a copy of one that was originally found at that site. If you visit Pompeii when there are few clouds over Vesuvius, you can take a marvelous picture of the ruins with the volcano in the background. We had some clouds but the picture is below.