Complex sentence: When they finally reached Marcianople's gates, they were barred out by the city's military garrison and denied entry, and worse, the Romans unsuccessfully tried to assassinate the Goth leaders during a banquet.
Split into simpler sentences: When they finally reached Marcianople's gates, they were barred out by the city's military garrison and denied entry. What's more, the Romans unsuccessfully tried to assassinate the Goth leaders during a banquet.