After the youngest of the three Asen brothers, Kaloyan, was crowned Emperor in early 1197 he immediately showed his resolution to continue the war with the Byzantines by all means and liberate all Bulgarian lands.

At the turn of the new century he seized the strong castle of Constancia (near modern Simeonovgrad) and then struck in the opposite direction and besieged the last Byzantine stronghold to the north of the Balkan Mountains, Varna.

Varna was defended by a large garrison including western mercenaries who were known to be the bravest soldiers in the Byzantine army.

[1] To take the fortress the Bulgarian engineers constructed an enormous siege tower which was wider that the outer moat.

This action, carried out according to George Acropolites as revenge for the 14 thousand blinded Bulgarian prisoners of war by Emperor Basil II "the Bulgar Slayer" after the Battle of Klyuch in 1014,when the Bulgarian tsar Samuil was defeated, earned Kaloyan the moniker "the Roman Slayer".