Constantinople was besieged by: Ostrogoths (V century), Avars, Slavs and Bulgarians (VI century), Avars and Persians (VII century), Arabs (VII and VIII centuries), Kiev Slavs and Varangians (IX century), Bulgarians (X century), French, Venetians, Byzantines (XIII century), Ottoman Turks (XV century). The French (1204), the Byzantines (1261) and the Turks (1453) managed to take the city.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.