Complex sentence: During that year, he and Verus launched a new campaign against the Parthians, this time across the northern Tigris river, and into Media, and rumours (ultimately false) reached Rome that Cassius had crossed the Indus River along with the Third Syrian legion.
Split into simpler sentences: During that year, he and Verus launched a new campaign against the Parthians, this time across the northern Tigris river, and into Media. There, rumours (ultimately false) reached Rome that Cassius had crossed the Indus River along with the Third Syrian legion.