Among the 104 “covenants” (mvng ) in the Chun/Chyou (CC) chronicle, what distinguishes the 16 tung-mvng (Legge “covenanted together”)? The commentaries give no convincing answer.1 But there must have been some feature that made these covenants different for those entering into them. On considering the political context, I find that the tung-mvng covenants were a sort of collective security agreement, meant to enforce solidarity among the northern states against the military threat from southern and non-Sinitic Chu. I also note that this north/south polarity virtually defines the middle period of Spring and Autumn.