During the ninth century A.D. Bulgaria once again became the focus of Greek and Roman cultural and political rivalry. The dispute was finally terminated when Bulgaria, under King Boris I, accepted Christianity from Constantinople rather than from Rome. As early as 836 the Byzantine Empire had sent two brothers, Cyril and Methodius, to convert the Slavs. When the brothers were in Venice, they argued in favor of church services and literature in the Slavic language, opposing the Roman bishops who believed that only Hebrew, Greek, and Latin were suitable languages for worship. This dialogue further exacerbated the tensions between Byzantium and Rome. By 870 Boris made Orthodox Christianity the official religion of the state. At this juncture Bulgaria fell under the Byzantine sphere of influence, completing--for the moment--its break with the Roman religion and culture. The influence of Cyril and Methodius upon the Bulgarian language and culture is incalculable. They not only carried a new liturgical form to Bulgaria but also devised a new alphabet known as Cyrillic. This new alphabet soon replaced Latin and Greek as the only form of writing, and on its base a new Slavic literature and culture grew up. When Bulgaria adopted Christianity from Byzantium, it also adopted Byzantium's territorial ambitions. Under Tsar Simeon (A.D. 893-927), a period known as the Golden Age, Bulgaria extended its territories from the Black Sea in the east to the southern Carpathian Mountains in the north, to the Sava River in the west, and to Macedonia in the southwest. It was in this period that Bulgaria reached the peak of its territorial expansion, penetrating deep into the Byzantine Empire. Macedonia and Albania became Bulgaria's new frontiers; in 924 Serbia fell under Bulgarian rule. With these victories Simeon claimed the title tsar of all the Bulgarians and the Greeks. With the territorial expansion came a domestic flourishing in the arts and an increase in trade. The arts and architecture of the period were significant for their beauty and vitality. Preslav, then the capital city, became the center of culture. Crafts, such as goldsmithing, pottery, stonemasonry, and blacksmithing grew, and shops sprang up everywhere. At the same time literature flourished, and education and scholarship took on a new importance. Knowledge of Slavic literature became widespread, and writers treated such varied topics as religion, grammar, logic, and patriotism.