Herodotus and other Greek authors about loyalty and betrayal in the besieged city This study attempts to determine the frequency of the betrayal of a besieged city in the world of Herodotus. The Histories is an excellent source of knowledge about the attitude of Greeks towards disloyal fellow citizens opening the city gates to the enemy, at a time when siege machines were not yet known, and betrayal (along with hunger and deception) was practically the only chance to conquer the city. Consequently, the question arises: do broader historical and literary studies (testimonies from subsequent decades and centuries) allow us to see the correlation between the popularity of the phenomenon of city betrayal and the development of siege technique. Was the role of betrayal decreasing with time when tools appeared that could assault the city walls? The article is an attempt to answer the question about the importance of loyalty to the local community in the face of war in the context of changing external conditions.