Purpose: I've been thinking about problems of goal advancement in spite of death, which brings us to honor. I am also keen on the history of Central Asia and the Steppe, and this is really cool: hence the blog section.
The word comitatus is Latin for retinue, or armed escort. In Germania, Tacitus uses it to describe the relationship between a lord and his sworn warrior. Through textual and archaeological evidence, this relationship has been shown to be widespread, and extended back much further to Proto-Indo-European times. It has been observed as far west as Spain, and as far east as Korea and Japan. I have most of this information from the book Empires of the Silk Road: A History of Central Eurasia from the Bronze Age to the Present, by Christopher Beckwith.
The comitatus is a lord and a warband of his friends, who swear to defend him to the death, forsaking all other obligations. In life they are bodyguards and constant companions, asking for and receiving gifts of wealth and weapons. If the lord dies first then his comitatus would be interred with him after ritual suicide or execution, and they were buried armed for battle in order that they could fight in the afterlife. Such was honor in those days.
The detail about this arrangement that seems most important to me is that the oath superseded obligations to their kin-group or people. Near as I can tell it is the first social institution to do this: while we have evidence of urbanization and religious organization which is earlier, they are not separated from kin-group concerns. It proved extremely resilient, lasting as late as early modern times in the Scandinavian and Islamic contexts (though I note that the pattern had been adapted - for example ritual execution and suicide fell into disuse with the rise of current world religions).
- Seems to have arisen concurrent with chariots; apart from methods of making tools, may be the earliest military innovation.
- I would expect success in competing against clan-oriented power bases, which was probably especially important for intra-clan competition.
- Reliant on a shared culture of honor.
- Bound up with commercial interests: being able to attract brave companions required wealth to give them, which meant it required profitable commerce, taxes, or plunder.
This pattern of oath-bound behavior has a variety of local terms, but because it comes from Central Asia and the Steppe Zone much of the textual sources available to us are in Arabic; there are a wide diversity of terms in Arabic which are all collapsed into the English word 'slave'. For example, the ghulam and mamluk are both translated as slave - but the former appears to be the Arabic version of the comitatus and the latter to be an institutionalized version of the same concept.