Kaloyan concluded an alliance with Theodore I Laskaris, Emperor of Nicaea. Laskaris had started a war against David Komnenos, Emperor of Trebizond, who was supported by the Latins. He persuaded Kaloyan to invade Thrace, forcing Henry to withdraw his troops from Asia Minor. Kaloyan laid siege to Adrianople in April 1207, using trebuchets, but the defenders resisted. A month later, the Cumans abandoned Kaloyan's camp, because they wanted to return to the Pontic steppes, which compelled Kaloyan to lift the siege. Innocent III urged Kaloyan to make peace with the Latins, but he did not obey.