The Battle of Pliska or Battle of Vărbitsa Pass was a series of battles between troops, gathered from all parts of the Byzantine Empire, led by the Emperor Nicephorus I, and the First Bulgarian Empire, governed by Khan Krum. The Byzantines plundered and burned the Bulgar capital Pliska which gave time for the Bulgarians to block passes in the Balkan Mountains that served as exits out of Bulgaria. The final battle took place on 26 July 811, in some of the passes in the eastern part of the Balkans, most probably the Vărbitsa Pass. There, the Bulgarians used the tactics of ambush and surprise night attacks to effectively trap and immobilize the Byzantine army, thus annihilating almost the whole army, including the Emperor. After the battle, Krum encased the skull of Nicephorus in silver, and used it as a cup for drinking. This is one of the most documented instances of the custom of the skull cup. The Battle of Pliska was one of the worst defeats in Byzantine history. It deterred Byzantine rulers from sending their troops north of the Balkans for more than 150 years afterwards, which increased the influence and spread of the Bulgarians to the west and south of the Balkan Peninsula, resulting in a great territorial enlargement of the First Bulgarian Empire. Initial campaigns When Nicephorus became emperor in 802, he planned to reincorporate Bulgar-held territory back into the empire. In 807 he launched a campaign but only reached Adrianople and achieved nothing because of a conspiracy in his capital. That attempted attack, however, gave reason for the Bulgar Khan, Krum, to undertake military operations against the Byzantine Empire. The main objective was an extension to the south and south-west. The next year, a Bulgar army penetrated the Struma Valley and defeated the Byzantines. The Bulgar troops captured 1,100 litres (roughly 332 to 348 kilograms) of gold and killed many enemy soldiers including all strategoi and most of the commanders. In 809, Krum personally besieged the fortress of Serdica and seized the city, killing the entire garrison of 6,000. Preparation for an invasion In 811, Nicephorus organized a large force in an attempt to conquer Bulgaria once and for all. The army included forces from the Anatolian and European themata, and the Imperial Bodyguard (the tagmata). In addition, the army was joined by a number of irregular troops who expected a swift victory and the