A babban birni a siyasance da kuma a gwamnatance shi ne birnin da yake da matsayi na farko ko na hukuma a cikin ƙasa, lardi ko jiha, a matsayin wurin zaman gwamnati. Kalmar "capital" ta samo asali ne daga kalmar Latin "caput" (ma'ana 'kai'), amma a Falasdinu ta Byzantine mai magana da Girkanci, kalmar Girka da ake amfani da ita ga manyan birane ita ce "metropolis". Wasu manyan birane, kamar Urushalima, sun kasance kuma cibiyoyin addini. Haka kuma, a ƙarƙashin Musulunci an sami tsarin manyan birane biyu na siyasa da gwamnati a lokacin kololuwar Daular Abbasiyawa: Bagadaza da Ar-Raqqa (a Siriya ta yau), a zamanin Harun al-Rashid, tsakanin 796 zuwa 809 AD.

Politically and administratively a capital city is the city enjoying primary or official status in a country, province or state as a seat of government. The word capital derives from the Latin caput (‘head’), but in Greek-speaking Byzantine Palestine the Greek term for capital cities was metropolis. Some capital cities, such as Jerusalem, were also religious centres. Furthermore, under Islam an arrangement of joint political and administrative capitals existed at the height of the Abbasid Caliphate: Baghdad and al-Raqqa (in modern Syria), under Harun al-Rashid in 796‒809 AD.