The Bulgars of Asparuh moved westwards to what is now Bessarabia, subdued the territories to the north of the Danube in modern Wallachia, and established themselves in the Danube Delta. In the 670s they crossed the Danube into Scythia Minor, nominally a Byzantine province, whose steppe grasslands and pastures were important for the large herd stocks of the Bulgars in addition to the grazing grounds to the west of the Dniester River already under their control. In 680 the Byzantine Emperor Constantine IV (r.668-685), having recently defeated the Arabs, led an expedition at the head of a huge army and fleet to drive off the Bulgars but suffered a disastrous defeat at the hands of Asparuh at Onglos, a swampy region in or around the Danube Delta where the Bulgars had set a fortified camp. The Bulgars advanced south, crossed the Balkan Mountains and invaded Thrace. In 681, the Byzantines were compelled to sign a humiliating peace treaty, forcing them to acknowledge Bulgaria as an independent state, to cede the territories to the north of the Balkan Mountains and to pay an annual tribute. In his universal chronicle the Western European author Sigebert of Gembloux remarked that the Bulgarian state was established in 680. This was the first state that the empire recognised in the Balkans and the first time it legally surrendered claims to part of its Balkan dominions. The Byzantine chronicler Theophanes the Confessor wrote of the treaty: