Siege of Petra (550–551)
Based on advice from the Sabirs, their nomadic allies, the Byzantines constructed a type of lightweight battering ram that could be deployed on the sloped plain leading to the walls.
During the fighting, the wooden tower from which the defenders were frantically throwing their bombs accidentally caught on fire, causing the Sasanian defense to collapse.
After an unsuccessful attempt to break the gate, the Sasanians managed to destroy a tower through mining and breach the fort, forcing the Byzantine garrison to capitulate.
[7][8][9] While Bessas began the assault, the five-year truce of 545 had already expired in April 550 and Khosrow's envoy, Izad Gushnasp, was negotiating in Constantinople.
[12] The number of the installed garrison was 3,000 in 549, but in 550 it was 2,600 or 2,300 (according to Peterson); the rest were probably assigned to lesser fortifications or were busied with duties outside the fort such as foraging, scouting, or escorting.
[17][18] At this time a group of nobles of the Sabirs (a warlike nomadic people native to the Caucasus) visited the Byzantine camp in order to receive a sum of money from an envoy of Justinian.
Seeing the situation of the Byzantines, the Sabirs revealed to them a simple but ingenious way to batter a wall in sloped places: instead of using beams and wheels which made the frame heavy, they used woven osier twigs covered with hides as the protective frame, making the machine light enough to be carried by forty men on a sloped plane.
[17][19][20][21][a] According to the Byzantine historian Procopius, the Sasanian garrison placed a pre-made wooden "tower" on the wall and from there fully-armored men hurled fire pots containing a particular mixture of sulfur, pitch, and naphtha (a composition called the "oil of Medea") onto the top of the rams.
According to Petersen, these men were probably operating a traction trebuchet, and this "wooden tower" that is spoken of by Procopius was a frame that protected pulling crews from enemy fire.
The armored men with poles with hooks that accompanied the rams showed another functionality here, as they quickly pulled off the flaming projectiles from the roof of their machines to prevent serious damage.
Bessas fell too, but before the Sasanians could shoot him with arrows, his guards (doryphoroi) formed a testudo around him, and as he ordered, dragged him by the leg to a safe place, as he was both old and obese.
The Sasanians declared themselves ready to capitulate and asked for some time, but since both sides were still fighting, Bessas did not trust them and refused to stop the assault.
The fire gradually spread by naphtha leakage and finally consumed the whole wooden structure together with the armored men inside it, the charred bodies of whom fell over the attackers and the defenders.
[30][32] The next day, the 500 Sasanian forces who had shut themselves in the acropolis refused to surrender, in spite of an offer of capitulation, preferring instead a heroic death.
Bessas pressed on negotiation by sending a soldier to the wall to persuade the defenders by an exhortation, making references to Christian pity, but this failed too.
He resorted to force by torching the citadel by means of throwing incendiary materials, hoping that the Sasanians would surrender, but they decided to stay and perish in the flames.
[19] While a relief force under Mihr-Mihroe consisting mostly of cavalry and eight elephants was on their way to yet again relieve Petra, they did not arrive in time, only receiving the news of its fall in the spring of 551.
[7] The Byzantine forces in Lazica withdrew west to the mouth of the Phasis, while the Lazi, including their king Gubazes and his family, sought refuge in the mountains.
