Comitatus was a Germanic friendship structure that compelled kings to rule in consultation with their warriors, forming a warband. The comitatus, as described in the Roman historian Tacitus's treatise Germania (98.AD), is the bond existing between a Germanic warrior and his Lord, ensuring that neither leaves the field of battle before the other. The translation is as follows:

Comitatus, being the agreement between a Germanic lord and his subservients (his Gefolge or host of followers), is a special case of clientage and the direct source of the practice of feudalism. Partly influenced by the Roman practice, exemplified in the Marian Reforms initiated by Gaius Marius, of a general distributing land to his officers after their retirement, the Germanic comitatus eventually evolved into a wholesale exchange between a social superior and inferior. Comitatus is an Indo-European concept that predates Roman times and was practiced from Western Europe to China, especially among Eur-Asian Steppe tribes. The social inferior (in Feudalism, the Vassal) would pledge military service and protection to the superior (Lord). In return, the superior would reward the inferior with land, compensation, or privileges.