The Bulgarian delegates then meet the Ottomans for negotiations in Constantinople. Bulgaria's hope to regain lost territories in Eastern Thrace, where the bulk of Bulgarian forces had struggled to conquer and many died, was dashed as the Turks retained the lands they had regained in the counter-attack. The straight line of Ainos-Midia was not accepted for the eastern Border; the regions of Lozengrad, Lyule Burgas-Buni Hisar and Adrianople reverted to the Ottomans. After this Treaty of Constantinople, 30 September 1913, Bulgaria sought an alliance with the Ottoman Empire against Greece and Serbia (in support of their claims to Macedonia).