Croatia is a former Yugoslav republic on the Adriatic Sea. It is about the size of West Virginia. Part of Croatia is a barren, rocky region lying in the Dinaric Alps. The Zagorje region north of the capital, Zagreb, is a land of rolling hills, and the fertile agricultural region of the Pannonian Plain is bordered by the Drava, Danube, and Sava Rivers in the east. Over one-third of Croatia is forested. Croatia, at one time the Roman province of Pannonia, was settled in the 7th century by the Croats. They converted to Christianity between the 7th and 9th centuries and adopted the Roman alphabet under the suzerainty of Charlemagne. In 925, the Croats defeated Byzantine and Frankish invaders and established their own independent kingdom, which reached its peak during the 11th century. A civil war ensued in 1089, which later led to the country being conquered by the Hungarians in 1091. The signing of the Pacta Conventa by Croatian tribal chiefs and the Hungarian king in 1102 united the two nations politically under the Hungarian monarch, but Croatia retained its autonomy.