Siege of Constantinople (626)

The Siege of Constantinople in 626 by the Avars, aided by large numbers of allied Slavs and the Sassanid Persians, ended in a strategic victory for the Byzantines. The failure of the siege saved the Empire from collapse, and, combined with other victories achieved by Emperor Heraclius (r. 610–641) the previous year and in 627, enabled Byzantium to regain her territories and end the destructive Roman-Persian Wars by enforcing a favorable treaty with borders status quo circa 590.

• http://en.wikipedia.org/wiki/Siege of Constantinople (626)