Who the Emperor was who was "the last that ware the imperial diadem of Rome" is never stated.
To be sure, Bassianus calls himself "Caesar's son," but this is not a reference to Julius Caesar (see page I-253) or Octavius Caesar (see page I-292). All Roman emperors were called "Caesar," for that was one of the royal titles (see page I-390).
In fact, the identity of the just-dead Roman Emperor couldn't possibly be determined, for the entire play is a weird amalgamation of different periods of Roman history. There is a panoply of senators, tribunes, and common Romans on stage, as though it were of the stern period of the Roman Republic, as in Coriolanus. On the other hand, we have emperors, of a later period, and barbarian invaders of a still later period.
The names of the sons have some points of interest. The only important Saturninus in real Roman history was a radical politician who was killed about 100 b.c. in the years when the Roman Republic began the public disorders that were eventually to kill it. As for Bassianus, the name of the younger son, that is to be found among the names of three of the emperors of the dynasty of Septimius Severus, who ruled in the early third century.
The elder son of Septimius Severus was Bassianus. He succeeded on his father's death in 211. Bassianus did not rule under that name but was universally called "Caracalla," a nickname derived from the long cloak (caracalla) he habitually wore.
Bassianus had a younger brother, Geta, who was supposed to have inherited the emperorship along with him. The two brothers were deadly enemies, however, and by 212 Bassianus had killed Geta under particularly cruel circumstances.
Thus, the competition between Saturninus and Bassianus in the play seems to reflect, faintly, the competition between Bassianus and Geta in history.
In one respect, in fact, the time of Caracalla might be thought to be the latest period in which the play could be set, for it treats of a thoroughly pagan Rome. There is no sign of Christianity in the play, yet after Cara-calla's time, the growth of Christianity would have made the new religion impossible to ignore.
There are, however, other aspects of the play that make the time of Caracalla far too early.
As it happens, there is in existence a tale called The Tragical History of Titus Andronicus, of which the only known copy was published about a century and a half after Shakespeare's play was written. That copy may, however, be a reprint and the original may have appeared early enough to serve as Shakespeare's source.
In the booklet the time is set in the reign of Theodosius, by whom is probably meant the most famous Emperor of that name, Theodosius I. He ruled from 379 to 395, nearly two centuries after Caracalla.
When Theodosius died, he left behind two sons, but these, unlike the sons of Septimius Severus (or those in the play), did not compete for the throne. They inherited the co-emperorship in peace, with the elder, Arcadius, ruling the Eastern half from Constantinople, and the younger, Honorius, ruling the Western half from Rome.
To be sure, by the time Theodosius was Emperor, Rome was thoroughly Christian and Theodosius himself was particularly pious in this respect, so that the paganism of the play would then become an anachronism. (On the other hand, considering the horrible events that take place in it, the existence of Christianity would be embarrassing.)
... surnamed Pius
It turns out that there are factions in Rome who want neither son of the old Emperor, but who turn instead to a valiant general. The announcement is made by Marcus Andronicus the tribune, who happens to be a brother of that general. He says:
Know that the people of Rome, for whom we stand
A special party, have by common voice,
Chosen Andronicus, surnamed Pius
For many good and great deserts to Rome.
- Act I, scene i, lines 20-23
Andronicus is the Titus Andronicus of the tide. The surname of "Pius" was sometimes used in Roman history to indicate a man who was devout and who honored his parents and his gods. The most famous case of such a usage is that of Emperor Antoninus Pius, who reigned from 138 to 161 and whose reign saw the Roman Empire at its most peaceful.
... the barbarous Goths
The special claim of Titus Andronicus to the gratitude of Rome lay in the wars he had been fighting. Marcus says: