The Roman Temple of Elst (between Arnhem and Nijmegen in the Netherlands) must have been one of the largest north of the Alps. The site was already venerated before the Romans settled the Batavians in this area, and the site remained in use as a site of religious significance: today, it is the main church of Elst. When this Christian monument was bombed during the Second World War, the pagan shrine was discovered. It was apparently built at the beginning of our era, and reconstructed when Trajan visited the area in c.100.
The second sanctuary was made of natural stone, measured 23 x 30 meters, and must have had a height of 17 meters – comparable to a modern building of four or five stories. The temples of a typical Italian town like Pompeii were smaller and were erected from bricks, which suggests that the god of Elst was very important indeed.
Which god it was, is not known. Yet, it is certain that he was identified by the Romans with one of their own gods, because near the sanctuary, the remains of a traditional Italian sacrifice were found, a suovetaurilia. The only deities who received this triple offering of pig, sheep and bull were Mars and Mater Matuta (the male and female deities of fertility).
It is possible that the Romans identified him with their Hercules, because the remains of a statuette have been found, which show the club of this demigod. Since the supreme god of the Batavians, Magusanus, was equaled to Hercules, it is very tempting to think that Magusanus was venerated in the Elst temple. However, Hercules is not really known as a fertility god.
The site is open to the public, but you must make an appointment. The website of the Protestant Church contains this page on the history of the monument; I can not give a phone number as that may change. The church is about five minutes from the little railroad station.