Complex sentence: Inanna has a central role in the myth of "Enmerkar and the Lord of Aratta", which centers around the rivalry between the rulers of Aratta and Uruk for the heart of Inanna.
Split into simpler sentences: Inanna has a central role in the myth of "Enmerkar and the Lord of Aratta". A major theme in the narrative is the rivalry between the rulers of Aratta and Uruk for the heart of Inanna.