The year 476 is most often used as the marker for the end of the Roman Empire, but it is only the most common date used out of a number that could be used – after all, it is a complex issue. It was only the western half of the Roman Empire that fell in 476 – the eastern Empire lasted for almost another thousand years, until 1453. But few historians really argue that 1453 was when the Roman Empire fell, because its nature during this time was distinctly different to earlier centuries. Plus, the namesake city of Rome was not even a part of this empire for most of its existence. Hence we differentiate by calling this the Byzantine Empire. But the nature of the Roman Empire also changed before 476. It is common to divide the Roman imperial period into the early Roman Empire, known as the Principate, and the late Roman Empire, known as the Dominate. These names stem from the changing stylisation of imperial rule, but there are significant military, economic, religious, and social changes between the two periods as well. Yet we consider both periods to still be the Roman Empire because they shared more cultural elements than they did not. Should we then look at when these cultural elements fundamentally changed? Henri Pirenne believed that Roman culture elements in the Mediterranean world lasted well into the eighth century. But I do not know of any historians arguing that the Empire continued through the succeeding barbarian kingdoms! These are just some of the alternatives to 476 that could be used.

So why do most historians still stick with 476? I think the best way to understand why is not by asking what was unique about Odoacer’s Kingdom, but by looking at the unique changes that occurred to the Empire itself. Any of the successor kingdoms, or the generalissimos like Stilicho and Ricimer, or rebels like Alaric, could have achieved what Odoacer did, which was remove the Roman emperors from power. In 475, Orestes, a general of Pannonian descent and therefore illegible to be emperor himself, appointed his son, Romulus Augustulus, as a puppet emperor. Orestes upset relations with the foederati commander Odoacer, who revolted and killed Orestes. Odoacer then advanced on Ravenna, Romulus’ imperial capital. Romulus Augustulus surrendered and abdicated and was allowed to live on a pension in southern Italy. The fact that Odoacer then ruled as a patrician or Rex, without appointing himself or someone else as a Roman emperor, is the indicator most historians use as the line-in-the-sand that defines the end of the Roman Empire.

It would be remiss of me to not include that there are still problems with the use of this date. There are two major ones: the continued reign of Julius Nepos, and whether the imperial office is actually the most significant part of Roman administration. Julius Nepos was appointed Roman emperor in 474 by the eastern emperor Leo I. This was a short-lived reign, because in 475 it was Orestes who advanced on Ravenna to overthrow the emperor. Nepos, unlike Romulus Augustulus, did not surrender, instead choosing to flee to Dalmatia where he continued to rule as emperor, even after Odoacer became king. Nepos even received nominal recognition from Zeno and Odoacer as the western Roman emperor. However his power in reality was minimal – Nepos did not exert control over any territory other than Dalmatia, and would be executed by his own soldiers in 480. Dalmatia would then be conquered by Odoacer. Nonetheless, Nepos was truthfully the last western Roman emperor.

For the second problem, using the deposition of the emperor to signal the end of the Empire is not necessarily fair to the rest of the imperial political body. For most of the imperial period the emperors were the most powerful and influential individuals. But during the fifth century this had dramatically changed. From Theodosius’ death in 395 the Roman Empire had been ruled by successive puppet emperors controlled by a series of generalissimos. So truthfully, the death of Orestes was more important than the removal of Romulus Augustulus. Odoacer retained many of the other elements of Roman political administration, such as the Senate. He also continued carrying out other responsibilities of the emperors. To quote a comment made by our moderator u/shlin28:

It is only a brief anecdote from only one part of the frontier, but it paints a rather grim picture and has long been used by historians to illustrate the rise of 'barbarian' power. A little later, however, the story adds another interesting caveat to this narrative: Later, Odoacer heard that Fredericus [king of the Rugii, his enemy] had returned to his home. At once he dispatched a great army, under his brother Onoulfus; before whom Fredericus fled again, and went to King Theodoric, who was then at Novae, a city of the province of Moesia. Onoulfus, however, at his brother's command ordered all the Romans to migrate to Italy. Then all the inhabitants, led forth from the daily depredations of the barbarians as from the house of Egyptian bondage, recognized the oracles of Saint Severinus [who had predicted this]. The key point here is that the Roman inhabitants of Noricum were evacuated by Odoacer, the 'post-Roman' king of Italy. We also learn from the same chapter that someone with the title of 'Count', a very Roman office, was involved, so all in all it suggests that Odoacer spent quite a lot of resources to evacuate and then settle the Romans in Italy. Odoacer may be a 'barbarian' general, but the forces he commanded after 476 had literally been parts of the Roman army and his rule relied on support from the Senate, the Italian landowners, and Constantinople. Viewed from this perspective, what was he doing that was not Roman, apart from his parentage?

You can see here that the loss of the emperor may not have changed many things for the Romans.

I think what makes historians overlook these things then comes down to convenience. It is easier to refer to a specific year of Odoacer deposing Romulus rather than trying to pin down a general time when Roman administrative or cultural elements had changed enough. Julius Nepos is forgotten for similar reasons of pragmatic convenience. Plus, he was a moderately embarrassing emperor, first fleeing his capital and then failing to set up a position of strength in Dalmatia. Also, it is perfectly poetic to have Rome’s last emperor be named after both the founder of Rome, and its first emperor.