Succeeding rulers strengthened the Bulgarian state throughout the 8th and 9th centuries. Krum introduced a written code of law and checked a major Byzantine incursion at the Battle of Pliska, in which Byzantine emperor Nicephorus I was killed. Boris I abolished paganism in favour of Eastern Orthodox Christianity in 864. The conversion was followed by a Byzantine recognition of the Bulgarian church and the adoption of the Cyrillic alphabet, developed in the capital, Preslav. The common language, religion and script strengthened central authority and gradually fused the Slavs and Bulgars into a unified people speaking a single Slavic language. A golden age began during the 34-year rule of Simeon the Great, who oversaw the largest territorial expansion of the state.