Complex sentence: The priest calculated the day, but, wanting the founding to fail, told Seleucus a different date, the plot failed however, because when the correct day came, Seleucus' soldiers spontaneously started to build the city.
Split into simpler sentences: The priest calculated the day, but, wanting the founding to fail, told Seleucus a different date. The plot failed however, because when the correct day came, Seleucus' soldiers spontaneously started to build the city.