Emperor Isaac II Angelos had been forced to conclude a true after his second campaign in Moesia and the fruitless siege of Lovech in 1187, thus de facto recognizing the independence of Bulgaria.

Until 1189, both sides had observed the truce.

The Bulgarians had used this time to further organize their administration and military.

When the soldiers of the Third Crusade reached the Bulgarian lands at Niš, Asen and Peter had offered to help the Emperor of the Holy Roman Empire, Frederick I Barbarosa, with a force of forty thousand against Constantinople.

The relations between the Crusaders and the Empire have smoothed, however, and the Bulgarian proposal had been evaded.

Constantinople prepares a third campaign to avenge the Bulgarian actions.

Like the previous two invasions, they manage to overcome the passes of the Balkan mountains.

They make a bluff, indicating that they would pass near the sea by Pomorie, but instead head west and pass through the Rishki Pass to Preslav.

The Byzantine army next marches westwards to besiege the capital at Turnovo.

At the same time, the imperial fleet reaches the Danube in order to bar the way of Cuman auxiliaries from the northern Bulgarian territories.

The defense of the city is led by Asen himself and the morale of his troops is very high.

The Greeks’ morale, on the other hand, is quite low for several reasons: the lack of any military success, heavy casualties and particularly the fact that the soldiers' pay is in arrears.

This is used by Asen, who sends an agent in the guise of a deserter to the imperial camp.

The man tells Isaac II that, despite the efforts of the imperial navy, an enormous Cuman army has passed the river Danube and is heading towards Tarnovo to relive the siege.

The Emperor panics and immediately calls for a retreat through the nearest pass.