Neanderthal remains dating to around 150,000 years ago, or the Middle Paleolithic, are some of the earliest traces of human activity in the lands of modern Bulgaria.[17] Remains from Homo sapiens found there are dated c. 47,000 years BP. This result represents the earliest arrival of modern humans in Europe.[18][19] The Karanovo culture arose c. 6,500 BC and was one of several Neolithic societies in the region that thrived on agriculture.[20] The Copper Age Varna culture (fifth millennium BC) is credited with inventing gold metallurgy.[21][22] The associated Varna Necropolis treasure contains the oldest golden jewellery in the world with an approximate age of over 6,000 years.[23][24] The treasure has been valuable for understanding social hierarchy and stratification in the earliest European societies.[25][26][27] The Thracians, one of the three primary ancestral groups of modern Bulgarians, appeared on the Balkan Peninsula some time before the 12th century BC.[28][29][30] The Thracians excelled in metallurgy and gave the Greeks the Orphean and Dionysian cults, but remained tribal and stateless.[31] The Persian Achaemenid Empire conquered parts of present-day Bulgaria (in particular eastern Bulgaria) in the 6th century BC and retained control over the region until 479 BC.[32][33] The invasion became a catalyst for Thracian unity, and the bulk of their tribes united under king Teres to form the Odrysian kingdom in the 470s BC.[31][33][34] It was weakened and vassalised by Philip II of Macedon in 341 BC,[35] attacked by Celts in the 3rd century,[36] and finally became a province of the Roman Empire in AD 45.[37] By the end of the 1st century AD, Roman governance was established over the entire Balkan Peninsula and Christianity began spreading in the region around the 4th century.[31] The Gothic Bible—the first Germanic language book—was created by Gothic bishop Ulfilas in what is today northern Bulgaria around 381.[38] The region came under Byzantine control after the fall of Rome in 476. The Byzantines were engaged in prolonged warfare against Persia and could not defend their Balkan territories from barbarian incursions.[39] This enabled the Slavs to enter the Balkan Peninsula as marauders, primarily through an area between the Danube River and the Balkan Mountains known as Moesia.[40] Gradually, the interior of the peninsula became a country of the South Slavs, who lived under a democracy.[41][42] The Slavs assimilated the partially Hellenised, Romanised, and Gothicised Thracians in the rural areas.[43][44][45][46] First Bulgarian Empire Main article: First Bulgarian Empire Emperor Simeon I: The Morning Star of Slavonic Literature, The Slav Epic cycle by Alfons MuchaNot long after the Slavic incursion, Moesia was once again invaded, this time by the Bulgars under Khan Asparukh.[47] Their horde was a remnant of Old Great Bulgaria, an extinct tribal confederacy situated north of the Black Sea in what is now Ukraine and southern Russia. Asparukh attacked Byzantine territories in Moesia and conquered the Slavic tribes there in 680.[29] A peace treaty with the Byzantine Empire was signed in 681, marking the foundation of the First Bulgarian Empire. The minority Bulgars formed a close-knit ruling caste.[48] Succeeding rulers strengthened the Bulgarian state throughout the 8th and 9th centuries. Krum introduced a written code of law[49] and checked a major Byzantine incursion at the Battle of Pliska, in which Byzantine emperor Nicephorus I was killed.[50] Boris I abolished paganism in favour of Eastern Orthodox Christianity in 864. The conversion was followed by a Byzantine recognition of the Bulgarian church[51] and the adoption of the Cyrillic alphabet, developed in the capital, Preslav.[52] 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.[53][52] A golden age began during the 34-year rule of Simeon the Great, who oversaw the largest territorial expansion of the state.[54] The literature produced in Old Bulgarian soon spread north from Bulgaria and became the lingua franca of the Balkans and Eastern Europe.[55][56][57][58][59] The political, cultural, and spiritual power of the Bulgarian Empire during the Krum's dynasty turned Bulgaria into one of the three superpowers in Europe at that time, alongside the Byzantine Empire and the Carolingian Empire of the Franks, which would later become the Holy Roman Empire.[60] Ruins of Pliska, capital of the First Bulgarian Empire from 680 to 893 After Simeon's death, Bulgaria was weakened by wars with Magyars and Pechenegs and the spread of Bogomilism.[53][61] Simeon's successor Peter I negotiated a favourable peace treaty. The Byzantines agreed to recognize him as Emperor of Bulgaria and the Bulgarian Orthodox Church as an independent Patriarchate, as well as to pay an annual tribute.[62][63][64] The peace was reinforced with a marriage between Peter and Romanos's granddaughter Irene Lekapene.[63][65