Islamic Calendar and Arabian Markets
Bonner's most important source is the "Tradition of the Markets," extant in a number of texts from the 9th century and later. This describes a market cycle spiraling around the peninsula throughout the year, with each market happening at a certain calendrical time. Bonner also notes accounts that the pre-Islamic Arabian calendar was similar to the Jewish in that an additional month was occasionally added to keep it in line with the seasons. Because these accounts serve to harmonize months with the seasons in ways that place certain coastal market fairs in line with the arrival of ships sailing with seasonal monsoons, Bonner convincingly finds them creditable.
These markets were dominated by various elites, whether Sasanian governors or noble Arab lineages. These elites would dominate the markets by selling their own goods first, effectively setting prices favorable to themselves. The markets also featured forms of silent trade, which allowed for the prevention of tribal feuding by concealing identities, as well as concealing the profit-making which could be seen as dishonorable in a culture that valued generosity. Noble lineages competed for the favors of elites above them, while also seeking to increase their status through ostentatious gift-giving based on the previous profiteering.
The key to Bonner's theory is that by banning the adding of an intercalary month to keep the dates of the fairs in line with the seasons, they began drifting throughout the year unmoored from the monsoon season which anchored those along the coast. The ban also disempowered those who were charged with control of the calendar; I myself wondered if this control was somehow also linked with pre-Islamic Arabian religious beliefs and practices. In any event, with the decline of the fairs, an alternative moral order linked with increasing class stratification and self-aggrandizement through wealth disappeared from the peninsula.