Please note that Mommsen uses the AUC chronology (Ab Urbe Condita), i.e. from the founding of the City of Rome. You can use this reference table to have the B.C. dates
The citadel-hill,
the Byrsa (Syriac, birtha = citadel), a comparatively considerable
rock having a height of 188 feet and at its base a circumference
of fully 2000 double paces,(12) was joined to this wall at its
southern end, just as the rock-wall of the Capitol was joined
to the city-wall of Rome.
12. Oros. iv. 22. Fully 2000 paces, or--as Polybius must have
said--16 stadia, are=about 3000 metres. The citadel-hill, on which
the church of St. Louis now stands, measures at the top about 1400,
half-way up about 2600, metres in circumference (Beule, p. 22); for
the circumference at the base that estimate will very well suffice.
Its summit bore the huge temple of the
God of Healing, resting on a basement of sixty steps. The south
side of the city was washed partly by the shallow lake of Tunes towards
the south-west, which was separated almost wholly from the gulf by a
narrow and low tongue of land running southwards from the Carthaginian
peninsula,(13) partly by the open gulf towards the south-east.