Ceasar Diocletian began his campaign against the Sarmatians....

No, axes were used in warfare long before the medieval period.

The ancient Egyptians, Assyrians, Babylonians, Nubians, Persians, Sarmatians, Dacians and many other people used axes in battle, sometimes equipping entire units with this weapon.

Mariusz Mielczarek has written:

'Ancient Greek coins found in Central, Eastern, and Northern Europe' -- subject(s): Coins, Greek, Greek Coins

'The Sarmatians (Elite S.)'

'Cataphracti and Clibanari (Studies on the History of the Ancient & Mediaeval Art of Warfare)'

Diocletian began to reign A.D. 284 and once more revived the declining Roman Empire. He defeated the Sarmatians and Carpi during several campaigns between 285 and 299. Diocletian separated and enlarged the empire's civil and military services and reorganized the empire's provincial divisions, establishing the largest and most bureaucratic government in the history of the empire.

Derek Williams has written:

'The reach of Rome ; a history of the Roman imperial frontier 1st-5th centuries AD' -- subject(s): History, Boundaries, Fortification, Military art and science, Limes (Roman boundary)

'Romans and Barbarians' -- subject(s): History, Sources, Sarmatians, Roman influences, Boundaries, Celts, Civilization, Germanic peoples