Military duty in ancient Greece was perceived and practiced by citizens as an important component of civic duty as well as piety to the gods. The causes of war were usually political , naturally imbued with pious issues, and were also instigated by breaches in good faith between city-states. The citizen of ancient Greece was also a soldier, allowing him to engage in war and to become involved in civic duties. The predominant duty of the citizen was his participation in war, through which he was partaking in the act of defence of the values and honor of his city-state, regardless of whether the war was defensive or offensive.
Military duty also ran in accordance with piety to the gods, which also correllated with civic responsibilities. Piety to the gods appears to been important in warfare, in that the soldier felt it an obligation to uphold his courage and hardships in war as an act of piety; also, in defending a city state, a soldier was also protecting the city's overseer, either a god or goddess.
In essence, military duty was composed of two themes which were integrated into a whole institutional form of duty. Piety was upheld through sacrifices and obedience, which evolved on the battlefield through personal acts of piety by means of virtue and valour. Civic duties were instituted on the battlefield by the citizen's direct involvment in war, henceforth, spreading civil duties into the domain of military duties. The composition of the citizen's military duty was essentially the integration of pious and civil obligations into that duty, from which the city-state and its god both instituted a parallel function into military responsibilities.