On his arrival, he engaged Adarman near the city which he was attacking, defeated him, and drove him back into Persia.
In the ensuing spring, after another vain attempt at negotiation, the offensive was taken by the Persians, who, early in A.D.581, crossed the frontier under Tam-chosro, and attacked the Roman city of Constantia, or Constantina.

Maurice hastened to its relief; and a great battle was fought in the immediate vicinity of the city, wherein the Persians were completely defeated, and their commander lost his life.

Further advantages might have been gained; but the prospect of the succession drew Maurice to Constantinople, where Tiberius, stricken with a mortal disease, received him with open arms, gave his daughter and the state into his care, and, dying soon after, left him the legacy of the empire, which he administered with success for above twenty years.
On quitting the East, Maurice devolved his command upon an officer who bore the very common name of Johannes, but was distinguished further by the epithet of Mustacon, on account of his abundant moustache.
This seems to have been a bad appointment.

Mustacon was unequal to the position.

He gave the Persians battle at the conjunction of the Nymphius with the Tigris, but was defeated with considerable loss, partly through the misconduct of one of his captains.