The history of Yemen describes the cultures, events, and peoples of what is one of the oldest centers of civilization in the Near East. Its relatively fertile land and adequate rainfall in a moister climate helped sustain a stable population, a feature recognized by the ancient Greek geographer Ptolemy, who described Yemen as Eudaimon Arabia (better known in its Latin translation, Arabia Felix) meaning "fortunate Arabia" or "Happy Arabia". Yemenis had developed the South Arabian alphabet by the 12th to 8th centuries BC, which explains why most historians date all of the ancient Yemeni kingdoms to that era. Between the 12th century BC and the 6th century AD, it was dominated by six successive civilizations which rivaled each other, or were allied with each other and controlled the lucrative spice trade: Ma'in, Qataban, Hadhramaut, Awsan, Saba, and Himyar. Islam arrived in 630 AD, and Yemen became part of the wider Muslim realm. Ancient history With its long sea border between early civilizations, Yemen has long existed at a crossroads of cultures with a strategic location in terms of trade on the west of the Arabian Peninsula. Large settlements for their era existed in the mountains of northern Yemen as early as 5000 BC. Little is known about ancient Yemen and how exactly it transitioned from nascent Bronze Age civilizations to more trade-focused caravan kingdoms. The Sabaean Kingdom came into existence from at least the 11th century BC. There were four major kingdoms or tribal confederations in South Arabia: Saba, Hadramout, Qataban and Ma'in. Saba is believed to be biblical Sheba and was the most prominent federation. The Sabaean rulers adopted the title Mukarrib generally thought to mean "unifier", or a "priest-king". The role of the Mukarrib was to bring the various tribes under the kingdom and preside over them all. The Sabaeans built the Great Dam of Marib around 940 BC. The dam was built to withstand the seasonal flash floods surging down the valley. Between 700 and 680 BC, the Kingdom of Awsan dominated Aden and its surroundings. Sabaean Mukarrib Karib'il Watar I changed his ruling title to that of a king, and conquered the entire realm of Awsan, expanding Sabaean rule and territory to include much of South Arabia. Lack of water in the Arabian Peninsula prevented the Sabaeans from unifying the entire peninsula. Instead, they established various colonies to control trade routes. Evidence of Sabaean influence is