Constantine may have been the only pope to come from the Assyrian ethnic group — the same semitic tribe which created the Assyrian Empire which existed from the 24th through the 7th century BCE.
He was also the last pope to visit Constantinople until Pope Paul VI in 1967. Pope Constantine's trip was undertaken to settle a dispute between eastern and western Christianity with Emperor Justinian II. Constantine's ability to identify with eastern thinking probably made the negotiations go more easily.
Justinian's successor, Philippikos Bardanes, was an adherent of Monothelitism which Pope Constantine refused to support, leading to more problems, but Philippikos Bardanes didn't last long as emperor and peaceful relations were restored again.