When searching for Justinian I's life story, sites mentions a lot of the amazing things he did(Hagia Sophia, the corpus jurex, territorial expansion). However, did he do anything wrong, that would have accelerated Byzantium's fall under Ottoman rule?
This is a pure enthusiastic question, and I may be asking more of an open question, but Justinian I is one of my favorite people to read about.
Of course Justinian made mistakes, no-one is perfect and even if Justinian himself did not do anything wrong, some people would have interpreted his actions as mistakes from their perspective. Moreover, I don't think it is worthwhile discussing his career with regards to the Ottomans, since their rise happened nearly 1000 years after Justinian and it was the result of millions of other individuals and their actions that had barely any relation to the sixth-century emperor.
But yes, onto the mistakes. I'll provide a list, but remember that each of them can be interpreted in a different way. A brutal massacre can be a politically astute move, whilst theological compromises were often seen as the darkest kind of heresy. It really depends on what your perspective is. Here are a few that came to mind, though you will see that many of them are contradictory, yet these criticisms were all attested to in the contemporary sources:
The list can go on forever to be honest. Justinian was a complicated person and even now historians have utterly different views on him. For O'Donnell (Ruin of the Roman Empire, 2008) and many others, Justinian's wars effectively destroyed Roman society in the west. Others can however note the role of the plague and how the economy of the western Mediterranean had been declining for decades by then. It is also possible to blame Justinian for Roman military failures and for bureaucratic corruption that led to numerous revolts, but again, was it due to Justinian or was it due to his subordinates? The Nika Riots (or the Nika Revolt as some historians like to call it) are similarly interesting, since it is debatable whether it was caused by Justinian's reforms and if the unrest was the inevitable result of simmering social tensions within the capital.
For myself, it is clear that Justinian had his failures and his successes, and that we have to evaluate his reign in stages. The first decade was broadly a success, since he successfully ended the Persian war, clamped down on dissent within Constantinople by both the elite and the common people, as well winning a few stunning victories against the Vandals and the Ostrogoths. His legal reform programme was also implemented remarkably quickly, so he was clearly a man with a plan and very ambitious. This was all done even though there was strong institutional opposition - many aristocrats looked down at the ex-peasant, whilst some of the bureaucrats were not fans of his changes. Then there were the religious dissenters, as many Romans in Egypt and Syria were miaphysite Christians and cannot have been overly pleased with the emperor, who was a follower of the Chalcedonian brand of Christianity.
The period from the 540s onwards was however pretty disastrous. The Persians launched a surprise attack and sacked Antioch, a defeat that was partially aided by Justinian's military focus on the west since it left the east less well-defended, whilst the plague struck the empire and killed off a good chunk of the population. The Gothic War also dragged on and on, a fact partially helped by Justinian's plan to run the war - he was suspicious of the military leadership after various conspiracies against him and so ensured that no-one had enough forces to actually win the war against a determined enemy. Similarly in North Africa the corrupt administration alienated the locals and led to many revolts in the following years. Justinian in this period also negotiated with the miaphysites to try to bring them back into the imperial fold, but failures occurred more often than successes.
The 550s saw some stunning successes, but also some major failures. The Gothic War was successfully concluded and the North African revolts were stamped out, but the cost was ruinously high. Justinian did manage to force through some of his religious compromises at the Fifth Ecumenical Council, but at the same time it alienated many Chalcedonian Christians in the west and brought reconciliation with the miaphysites no closer to reality. Theodora had also died in 548 and as her influence was evident in the emperor's legislative programme it must have been another blow. Another military failure was a Kutrigur attack that nearly reached Constantinople and disaster was only averted when Justinian brought Belisarius, a disgraced general, out of retirement to fight them off with a hastily raised force of volunteers. Throughout this period, there were also frequent earthquakes and conspiracies against the emperor, which even included people he had once favoured, such as Belisarius; all of them failed, but the number alone tells us a lot about Justinian's popularity. It was truly a grim period for the empire even though on the surface it was larger than ever. Justinian continued to hold power, but it was through brute force and excessive pageantry that he governed, not through genuine popularity.
The final years of Justinian's life were also problematic. The treasury was practically empty, yet spending continued for the endless war against Persia and tribute payments to the barbarians, many of whom were growing in power; the Persian War did end eventually, but it was a peace bought with cold hard cash and certainly not a glorious victory. There were more plots and even infighting between Justinian's supporters, as various family members competed to be his successor. A lone highlight of these years is perhaps the rebuilding of the dome of Hagia Sophia (which had collapsed in an earlier earthquake), but I do wonder whether this was just an empty gesture by an old emperor increasingly unable to fix the many real problems he faced. At the very end, Justinian even adopted miaphysite Christianity as his faith, a dramatic change from the orthodox emperor of the 520s. His legacy was problematic for his successors too, as his nephew Justin II deliberately abandoned Justinianic policies - he actively persecuted miaphysites, stopped payments to the barbarians and found an excuse to fight another war with Persia. For the new elites of the empire, Justinian was a tired old man who no longer cared about matters of state, to paraphrase a contemporary panegyric dedicated to the new emperor. Justinian may have been an energetic emperor in his youth, but in his old age he was the very opposite of the man imperial propaganda painted him as.
Justinian did many things right, but they were not nearly enough to maintain the empire's prosperity. He also did many things incorrectly, even though most of them were probably not as bad as our sources say, but the fact that they were seen as wrong by his contemporaries was enough to irreparably damage Justinian's reputation. Basically, calling Justinian a complicated man is one heck of an understatement and my summary here definitely did not do him justice, but I hope you have enjoyed this long read and are still interested in learning more about him!
Further reading:
The Cambridge Companion to the Age of Justinian (2005)
P. Bell, Social Conflict in the Age of Justinian: Its Nature, Management, and Mediation (2013)
J. A. S. Evans, The Age of Justinian: The Circumstances of Imperial Power (2000)
J. A. S. Evans, The Empress Theodora: Partner of Justinian (2002)
V. Menze, Justinian and the Making of the Syrian Orthodox Church (2008)
P. Sarris, Economy and Society in the Age of Justinian (2006)
Well, there were the Nika Riots...
On the leadup to some important peace negotiations with the Persians, violence between Chariot Racing teams (called just the "Blues" and the "Greens") led to some murders. This kind of violence was typical in Constantinople's largely oligarch/criminally owned sports world.
Just like modern-day UN summits, Justinian attempted to crush the unrest by arresting the major perpetrators of both teams. Unlike modern times, he sentenced them to death. this sparked riots from both sides, who demanded full pardon of the team-members. Justinian responded by announcing a new chariot race and commuting their sentences to imprisonment rather than execution.
This wasn't enough, and within a week half the city would burn from the riots that ensued from the Greens and the Blues. My professor at UConn likened this violence and destruction to modern-day soccer hooliganism, but much amplified. The "headquarters" of these riots was in the Hippodrome itself. Eventually, wealthy men took advantage of the chaos to try and have the mob crown a new emperor, a Green.
In order to regain control of the situation, Justinian bribed the leaders of the Blues with gold, saying that he favored them after all, and that they should not be working with the Greens. The Blues dispersed quietly, while Justinian's soldiers surrounded the Hippodrome. Following was one of the largest massacres in history, with as many as 30,000 rioters were killed if Procopius is to be believed. My professor, though skeptical of the numbers, estimated the act must have taken hours, the soldiers' arms getting exhausted from the all the killing.
Of course, after this event Justinian secured his rule and began his process of rebuilding and reuniting the empire... But it is certainly a ruthless and bloody chapter in his story.
Rosen, William. "Justinian's Flea". London: Penguin Books, 2008. Print.