Leaving a part of his forces to conduct this blockade, and with instructions to harass the Greek garrison by day and night, Bayezid, with the larger part of his army, marched through Bulgaria, and compelled the Prince of Wallachia to submit as a vassal of the Ottoman Empire. A part of his army then penetrated into Syrmia and engaged in war with the Hungarians. It was defeated and driven back, and Sigismund, the Hungarian King, was able to make a counter-attack, and to capture the important stronghold of Nicopolis. He, in turn, was forced to abandon the city, mainly by the assistance given to Bayezid by the Wallachians. It was during his retreat through the Duchy of Hunyadi that Sigismund met and became enamoured with Elizabeth Moronay. The offspring of this liaison was the celebrated Hungarian hero Hunyadi the Great, who later took such an active part against the Turks. In 1393, Bayezid sent an army, under command of his eldest son, Solyman, to invade the northern part of Bulgaria, which still enjoyed an autonomous existence. Tirnova, its capital, was taken by storm after a siege of three weeks. Its inhabitants were sent into Asia Minor as slaves. He then decided to incorporate the northern part of Bulgaria in the Ottoman Empire in the same manner as the southern part had already been treated. This completed the servitude of the Bulgarian people. Sisman, their prince, disappeared from the scene, and the ruling family became extinct. The land was confiscated, except in a few cases where the owners were allowed to become Moslems. It was parcelled out to Turks under a feudal system involving military service, while the cultivators of the soil were reduced to serfdom. About this time the fortresses of Nicopolis, Widdin, and Silistria fell into the hands of the Ottomans and opened the way into Hungary. Bayezid commenced a system of raids into that country, not for the purpose, at that time, of acquiring its territory, but for plunder. His Turkish ‘akinjis,’ or irregulars, spread terror over wide districts, burning and destroying villages and carrying off their inhabitants for sale as slaves. He fitted out ships also with the same object in the newly acquired ports in Asia Minor, and ravaged the islands of Chios and Negropont and districts on the coast of Greece.