  In an article written by Giulio Magli on the orientation of the Roman towns,
Bononia, the Roman Bologna, is given as a specific example to support Magli's
thesis on the existence of preferred solar alignments of the urban layout.
Assuming that the Roman towns had been oriented to the sunrise on a given day
of the year, Magli suggested possible preferred alignments according to Roman
festivals, in particular the festival of Terminalia. Of Bononia, we know the
date of foundation as Roman colony in 189 BC, given by Livy. We will show that,
according to Roman chronology and Republican calendar, it is impossible that
Bononia had been oriented to the sunrise on the day given by Livy. The
discrepancy is huge. Moreover, the direction of the decumanus cannot match the
dates of Terminalia for 189 BC. However, if we consider that the layout that we
see today is that of a recolonization under Octavian, we can have a certain
agreement between the direction of the decumanus and the sunrise on the day of
Terminalia (within three days), and a perfect agreement with the day of the
festival of Armilustrium. In the proposed discussion, we will stress in
particular the problem of the discrepancy between the historical dates of Roman
chronology and the Julian dates, those that we can find according to an
astronomical analysis. This problem is general and must be properly considered
in any archaeoastronomical analysis of Roman towns.
