Diocletian, as leader of the united East, is clearly the greater threat to Carinus.

Over the winter of 284–5, Diocletian has advanced west across the Balkans.

In the spring, some time before the end of May, his armies meet those of Carinus across the river Margus (Great Morava) in Moesia.

In modern accounts, the site has been located between the Mons Aureus (Seone, west of Smederevo) and Viminacium, near modern Belgrade, Serbia.

Carinus now proceeds to attack Diocletian, who would have been the loser had not Carinus been assassinated.

One account has him assassinated by a tribune whose wife he had seduced; in another, the battle is represented as having resulted in a complete victory for Diocletian, for Carinus' army had deserted him: this second account is also confirmed by the fact that Diocletian keeps Carinus' Praetorian Guard commander in service, though it is possible that Flavius Constantius, the governor of Dalmatia and Diocletian's associate in the household guard, had already defected to Diocletian in the early spring.

When the Battle of the Margus began, Carinus' prefect Aristobulus had also defected.

(Of the two dozen-plus emperors ruling Rome in the past fifty years, the lives of all but one have ended violently.)

Following Diocletian’s victory, both the western and the eastern armies acclaim him emperor.

Diocletian exacts an oath of allegiance from the defeated army and departs for Italy.

The area around present Belgrade, which had been ravaged by Attila the Hun in 442, had been taken by Theodoric the Great in 471.

As the Ostrogoths leave for Italy, the Gepids take over the city.

The old rivalry between the Gepids and the Ostrogoths having spurred up again, the Ostrogoths sack Belgrade on the Danube and Sava rivers in modern Serbia; …

…northwest to present-day Belgrade.

Local people in the Theme of Bulgaria rebel against the Empire in during the summer of 1040.

The uprising spreads and the rebels very quickly take over control over northern part of Pomoravlje and liberate Belgrade.

The origins of Peter Delyan are not clear.

He claims that he is a son of emperor Gavril Radomir and grandson of Samuel of Bulgaria, but he could also have been local who became the leader of an uprising against Constantinople’s rule over Bulgaria and claimed to be Samuel's grandson to justify his proclamation as Tsar Peter II of Bulgaria in Belgrade in 1040.

He is soon joined as co-ruler by Prince Alusian, a member of the ruling family, and leads Bulgarian forces in an open rebellion against Constantinople’s rule in a bid for independence.

The Hungarians occupy Belgrade in 1064, and …

Pecheneg troops pillage Syrmia (now in Serbia) in 1071.

King Solomon and Duke Géza, suspecting that the soldiers of the imperial garrison at Belgrade had incited the marauders against Hungary, decide to attack the fortress.

The Hungarian army crosses the river Sava, although the defenders "blew sulphurous fires by means of machines" against their boats.

The Hungarians take Belgrade after a siege of three months.

However, the imperial commander, Niketas, surrenders the fortress to Duke Géza instead of the king; he knows that Solomon "was a hard man and that in all things he listened to the vile counsels of Count Vid, who was detestable in the eyes both of God and men", according to the Illuminated Chronicle.

The division of the war booty causes a new conflict between Solomon and his cousin, because the king only grants a quarter of the booty to the duke, who claims its third part.

Hereafter the duke negotiates with the Emperor's envoys and sets all the imperial captives free without the king's consent.

The conflict is further sharpened by Count Vid: the Illuminated Chronicle narrates how he incited the young monarch against his cousins by saying that as "two sharp swords cannot be kept in the same scabbard", so the king and the duke "cannot reign together in the same kingdom".

…Belgrade and …

Emperor Conrad, accompanied by many German nobles, the Kings of Poland and Bohemia, and Frederick of Swabia, his nephew and heir, had departed Germany in May 1147.

On leaving Hungary and entering imperial Greek territory, he agrees to an oath of noninjury.

The Hungarian kingdom has occupied the Bulgarian province of Belgrade.