Complex sentence: The city was raided by the Sassanid Persians in the early 7th century, and following the conquest of the Holy Land by the Islamic armies in the 630s, the diocese and city suffered tremendously and steadily declined in size and importance.
Split into simpler sentences: The city was raided by the Sassanid Persians in the early 7th century. Following the conquest of the Holy Land by the Islamic armies in the 630s, the diocese and city suffered tremendously and steadily declined in size and importance.