Siege of Beograd (Premysloides Dynasty)

Background
While in Bosnia or Dalmatia, even in Serbian populated areas of these provinces, imperial reforms were welcomed and supported, in Serbia itself, reforms were reluctant accepted. Dissent against reforms was based on lose of kingdom independence after Mongolian raid and Imperial annexation and every each implemented reform led to curtail independence and weakening autonomous regime.

Situation worsened with election of new Serbian Governor in 1267, who was radical opponent of imperial reformation and while formally loyal to Emperor Romanos, he led various conspiracy to enstrenght his position. Imperial Intelligence, in that time oriented only on military and foreign affairs, was not able to recognize threat in Serbian Province and potential betrayal.

Siege
After defeat of Hungarians near Vas, Manuel Army replenished all forces and moved toward Serbia and Beograd. In that time, Manuel was already many months in negotiations with Serbian separatists and Serbian Governor, who promised support attackers during siege of Beograd. Governor bribed and persuaded most of Serbian-speaking garrison, which was also dissatisfied with Latin and Greek-speaking Roman officers. Serbian Governor himself was not in charge of defense, defense was under command of military governor Marianos, commander-in-chief of Imperial Army in Balkan, experienced and honorable commander.

When Manuel Army arrived and laid siege, Marianos commandeered his forces, while Serbian Governor armed local rebels and dissents and dug tunnels beneath fortification of Beograd to siege camp. 23 February, siegers started deceptive attack on besieged city and while most defenders were tied to repel attack, groups of Manuel troops used tunnels to pass through fortification and joined forces with Serbian rebels. When invaders emerged in center of Beograd, total chaos and violence burst out. Marianos was shocked and sent courier to Constantinople, but it was too late for Beograd. In few dozen minutes, invaders massacred defenders withing city center and besieged isolated barracks and pocket of resistance. City fall in few hours, after more then week of futile siege.

Aftermath
Fall of Beograd was shock for Imperial Government and Emperor, as well as for imperial military leadership. Inactivity and ineffectivness of fortification system, lack of communication, reinforcements, collapse of chain of command, execution of Marianos and collapse of Balkan Military District, it all led to declaration imperial emergency in realm and harsh restoring of military forces and assembling reinforcements and reserves to defend Thrakian Military District. Aside of all casualties, invaders and Serbian rebels killed 5,000 imperial officials, bureaucrats, merchants, advisors and their families stationed in Serbia to apply imperial reforms.