On August 17, 986, Samuel defeats the Byzantines at the Battle of Trajan's Gates. The Byzantine Emperor Basil II suffers the greatest defeat in his campaigns to conquer Bulgaria. A significant part of his army is destroyed, and he barely manages to save himself.
Before finally deciding on military action, Basil II tries to come to an understanding with the Bulgarians. In this context, he enters into negotiations with the elder of the remaining living comitopolis, Aron, aiming to create discord between him and Samuel. In exchange for his submission, Aron wants to establish family ties with the emperor through the marriage of one of his sons to Anna, the sister of Basil II. Instead of his sister, the emperor sends another bride to Aron. When the Bulgarians discovered the deception, a rift occurred in the negotiations and the emperor led his army against them.
Basil II set out on a campaign with an army of up to 30,000 men. From Adrianople (present-day Edirne), the emperor reached Philippopolis (present-day Plovdiv), and from there he headed for Serdica (present-day Sofia). His goal was to deal with the Bulgarians in one blow.
After the capture of Serdica, which, in addition to being the center of Aron's possessions, was also a strategic point between the northeastern and southwestern Bulgarian lands, Basil II planned to continue his campaign against Samuil southwest to Macedonia.
On his way to Serdica, around the Trajan's Gate pass, the emperor left a strong detachment led by the military commander Leo Melisinus with the task of guarding the rear of the main army. Reaching Serdica, Basil II surrounded it and built a heavily fortified camp.
Basil II found only about 4,500 defenders in the fortress, as Samuil was on a campaign with troops in Thessaly (Central Greece). This seemingly eased his task, but forced him to hurry before Samuil returned.
Samuil's troops arrived in the Sofia Field with an extremely fast march and settled under Vitosha in the area of the present-day village of Bistritsa in a fortified camp. From there, they carried out surprise attacks against the Byzantine troops, who were roaming the Sofia Field for food and fodder. Thus, instead of the Romans exhausting the besieged with hunger, they themselves began to starve.
The siege lasted 20 days. The Byzantine emperor headed back to Philippopolis again through the Trajan's Gate pass. Samuil did not set out to pursue him, but applied a "parallel pursuit" from Bistritsa through Dolni and Gorni Pasarel south of the Lozenska mountain range, in order to enter the Ihtiman field before the Byzantine troops and prepare an ambush for them.
The Byzantine army retreated from the Sofia field to Shtipon (present-day Ihtiman), where it spent the night. The rumor that the Bulgarians were blocking the surrounding mountain roads caused confusion among the soldiers and the next day the retreat continued in increasing disorder. Seeing this, the Bulgarians, led by Tsar Roman, Aron and Samuil, descended on the Byzantines, captured their camp and turned their retreat into flight.