The Byzantine Empire
The Emperors Invade
During the same years, Theodore of Epirus began moving into Thrace, taking Adrianople and Vizya, and at one point advancing up to Constantinople itself, only to withdraw. By 1226, the Latin Empire of Constantinople consisted of the city itself and not much more, plus the Greek duchies of Athens, Achaea, and the Archipelago. As these were largely independent, that Constantinople survived at all was largely because its enemies were as suspicious of each other as they were eager to recapture the Byzantine capitol. John Asen, Emperor of Bulgaria; Theodore, Despot of Epirus; and John Ducas, Emperor of Nicaea, each wanted to be the one to win the great prize. Each feared to risk too much too soon and lay himself open to attack from the others, and each worried that an open assault might stir up a Crusade against them.
The new emperor, Robert, gave them the opportunity for which they were waiting. He had taken a low-born woman as a lover. In 1227, his barons broke into the imperial bedchamber and mutilated the poor woman, and captured and drowned her mother. Robert went to Rome to appeal to Pope Gregory IX, but got little sympathy and was sent home. He died on the return trip, in 1228. His younger brother and heir, Baldwin II, was eleven years old. His sister Mary tried to rule with the help of a new bailie, but the empire was clearly vulnerable.
The barons now offered the crown to John of Brienne. John had once been King of Jerusalem but had been forced out by Frederick II. He was a claimant to the throne of Armenia. He was married to Berengaria, sister of King Ferdinand III of Castile, and was the father-in-law of Emperor Frederick II himself. He was at this moment (1228) commanding the papal army in Italy in Gregory IX's crusade against Frederick.
The deal offered was that John should come to Constantinople to be crowned emperor. He would serve for life, but when Baldwin II reached majority he would be crowned co-emperor. John's daughter Mary would marry Baldwin. Their heirs would become emperors; John's own heirs would be given various imperial fiefs. John accepted the offer, but did not arrive in Constantinople until 1231.
In the meantime, Theodore of Epirus had gone to war with Bulgaria. In 1230, at Klokotnitsa, John Asen completely defeated the Epirotes and captured Theodore. The Bulgarians swept across western Thrace, conquered Thessaly and much of Albania. In command of most of the Balkans and northern Greece, John Asen now began to call himself Emperor of the Bulgars and the Greeks. He was now openly trying to drive the Latins out, and made a treaty to this effect with the Nicaean emperor Vatatzes in 1235.
The two emperors met in Gallipoli and together invaded Thrace. Their combined armies marched on Constantinople and prepared to lay siege to the city. The situation was desperate, as Constantinople not only had no allies, she had virtually no army. John was unable to pay his mercenaries and most of them were gone, too. When he sallied out to meet the enemy, his army consisted of 160 knights. Even so, John of Brienne won a tremendous victory. At the same time, a Venetian fleet defeated the Nicaeans at sea, capturing twenty-five ships.
The two imperial allies soon began to suspect one another, and the great offensive fell apart. The situation was still precarious, however, and the young Baldwin II went to Rome to raise financial support. While he was gone, John of Brienne died in Constantinople on March 23, 1237.