The pleasant town of Assisi, with a population of just over 28.000 souls, is situated on the western slopes of the Monte Subasio. The town has Umbrian and Etruscan roots and was known as Asisium during the Roman era. In 89 BCE, Asisium was granted the status of a municipium and its inhabitants became Roman citizens. The most visible and tangible remains from the Roman era can found on the modern Piazza del Comune, the site of the ancient forum of the town. This is the spot where, next to the imposing medieval Torre del Popolo, we can admire the church of Santa Maria sopra Minerva. It is immediately clear that the building has not always been a Christian basilica. The pronaos or portico of an ancient pagan temple is still standing.
This temple was built in the first century BCE, possibly around the year 30 BCE. It was commissioned and financed by the quattuorviri – local magistrates – Gnaeus Caesius and Titus Caesius Priscus. There is hardly any evidence that the temple was dedicated to the Roman goddess of wisdom Minerva, as the name of the current church suggests. It is in fact a lot more likely that it was dedicated to Hercules, as a dedication stone mentioning this divine hero has been found. In this respect the current church can be compared to its namesake in Rome, which was built over part of a temple dedicated to Isis and Serapis rather than to Minerva. The pagan temple in Assisi was by no means a large building, but the six tall Corinthian columns of the pronaos are nevertheless impressive.
After the fall of the Roman Empire in the West, the temple was first converted into a church dedicated to San Donato. This church was deconsecrated later during the Middle Ages and converted into houses and shops. Still later, in the thirteenth century, it was used as the town hall and the seat of the commune. Part of the building was in use as a prison, as is evidenced by one of Giotto’s frescoes in the basilica of San Francesco elsewhere in Assisi: it clearly shows that the windows of the former temple and church have bars. The sturdy Torre del Popolo next to the current church was completed in 1305; Giotto’s aforementioned fresco is interesting in that it shows it only partially finished, so the fresco was certainly made before 1305.
The former temple of Hercules became a church again in the sixteenth century and was renamed the Santa Maria sopra Minerva. The original cella or inner chamber of the temple was completely demolished during this operation. In the seventeenth century the church was provided with a rich Baroque interior, which contrasts sharply with the exterior of the church.
Just west of the Piazza del Comune is a small archaeological museum which also gives access to the remains of the ancient Roman forum, which are nowadays far below street level. One of the most interesting items on display here is a model of the ancient temple from the Museo della Civiltà Romana in Rome. It clearly shows that the temple was built on a raised podium. The forum below had two entrances which gave access to stairs that led to the temple above. On the forum we also see a small sanctuary dedicated to Castor and Pollux. Between the columns, there would have been statues of the twin brothers and their horses. Behind their sanctuary, of the type known as a ‘tetrastyle’ temple, we see benches that were used by judges.
One of the raisons d’être of the museum seems to be to prove that the Roman poet Propertius was from Assisi (and not from Spoleto or Bevagna). On display are several tomb slabs with the name PROPERTIO chiselled into them. The remains of the (presumed) Casa di Properzio can be found underneath the church of Santa Maria Maggiore elsewhere in Assisi.
Sources four this post include my Dorling Kindersley and Royal Dutch Touring Club (ANWB) travel guides and Italian Wikipedia.
 Francesca Flores d’Arcais, Giotto, p. 32.