Question

what was justinian i's role in the decline of the byzantine empire

Answer 1

He overextended its military and drained its treasury. Justinian did some culturally significant things for the empire -- he expanded its borders, crushed a revolt against his rule, built churches and other public building projects, streamlined the laws of the empire. But in the long term, he wasn't very smart with his money or his military.

It's like a person that adds all of these rooms to your house and then leaves the next person to foot the bill. Only in this case, it would be the citizens of the empire and the next person on the throne.

In less than a century afterwards, most of the lands that expanded the empire were lost to outsiders (the military was overextended and then shrunk because the empire was running short on funds) and the treasury was suffered (because of his building projects and military expeditions).