Complex sentence: Archives of correspondence, whether for personal, diplomatic, or business reasons, serve as primary sources for historians and at certain times, the writing of letters has risen to the height of an art form and a genre of literature, for instance in Byzantine epistolography.
Split into simpler sentences: Archives of correspondence, whether for personal, diplomatic, or business reasons, serve as primary sources for historians. At certain times, the writing of letters has risen to be an art form and a genre of literature, for instance in Byzantine epistolography.