Samuel's armies attack the European possessions of the Empire, as the main effort of Basil II is concentrated against the rebel Skleros.

Samuel invades not only Thrace and the area of Thessaloniki, but also Thessaly, Hellas and Peloponnese.

Many imperial fortresses have fallen under Bulgarian rule.

Samuel wants to seize the important fortress of Larissa, which controls the key routes in Thessaly, and from 977 to 983, the town is blockaded.

After starvation forces the imperial garrison to surrender, the population is deported to the interior of Bulgaria and the males are forced to enlist in the Bulgarian army.

Although Basil II sends forces to the region, they are defeated, and the conquest of Larissa marks the loss of an important imperial stronghold in this part of the peninsula.

With this victory, Bulgaria has gained influence over most of the southwestern Balkans, although it does not occupy these territories.

From Larissa, Samuel takes the relics of Saint Achilleios, which are laid in a specially built church of the same name on an island in Lake Prespa.