The Sasanid Empire. Its largest extent is the one held on in the trilingual inscription of Shapur I. (240-272) at the „Tower of Zarathustra“ in Naqsh-i Rustam (not far from Persepolis, Fars, SW-Iran) made up in 260 AD. Shapur’s information are however strongly exaggerated and don’t always confirm the truth.
Note: The "Tübinger Atlas des Vorderen Orients" (TAVO) of the university of Tübingen (1993) was used for the delimitation of the Sasanid Empire about 270 AD.