From the first a difference was made between the apostles who had lived and worked within the existing boundaries of the Roman Empire, and those who had ended their lives in barbarian countries. In the far East, there was a second world-power similar to the Roman power in the West, _i.e._, the empire of the Parthians, or that earlier Persian Empire of the Achæmenides, which in its turn, again, had risen from the ruins of the ancient empires of Babylon and Assyria. The Jews had obviously numerous relations from old time with this Eastern Empire in consequence of their historical connection with it. After the return from exile, many Jews had remained there, and probably many others returned thither at a later time. In fine, the circumstances attending on the first Whitsunday show that many Jews were scattered throughout those provinces. The Eastern Empire consisted of a number of vassal states, which recognised a supreme sovereign, the King of Kings, but, in other respects, remained independent and sovereign, as for example, Armenia, whose inhabitants were moreover closely allied by blood with the Persians. The Jews, as Semites, had naturally more sympathy with these Easterns, once their ancient grievances had been forgotten, than they had with the Greeks and Romans who, at the beginning of the Christian era, were their oppressors. This explains why some of the apostles, some for life and others only temporarily, betook themselves thither, and spent their lives there in mission work and even ended their days in those parts. This is also the reason why we have so little reliable information concerning their life and work, and why the days of their deaths were not celebrated for so long a period in the West. The apostles who devoted themselves to the Eastern Empire were probably Bartholomew, Matthew, Thomas, Simon Zelotes, and Jude. Thaddeus also laboured there for a time in Mesopotamia and Osrhoëne. No traces remain of the labours of Matthias who is said to have preached to the Ethiopians, and of whose life, a writer of the ninth century, Autpert, Abbot of Monte Cassino, confesses nothing is known.[596] Several of the apostles have been commemorated from the first in the calendars, and always on the same day, while others, on the contrary, appear on different days in different parts of the Church, a circumstance which seems confusing to the historical investigator, but which can easily be explained when one has correctly grasped the principles which operate in liturgical matters. With regard to those who have everywhere been commemorated from the first on the same day, one can usually be certain that they died as martyrs in the Churches in question.