Complex sentence: In H.E.1.15 the adventus occurs within the period 449--55; in 1.23 and 5.23 another date, c.446, is given; in 2.14 the same event is dated 446 or 447.
Split into simpler sentences: In H.E.1.15 the adventus occurs within the period 449--55. In 2.14 the same event is dated 446 or 447.