All human cultures mark the passing of time / by the differences they observe / in the world around them.

Our choice of which differences to mark / depends firstly on what we can observe / and secondly on what is important in our lives.

How we mark the differences / ― the shapes of our calendars and our rituals ― / depends on the connections we make / between those two things.

In the agricultural society of pre-modern Europe, / where higher latitudes make the seasons easily observable, / it was natural to monitor the solar cycle.

Conversely, among the largely nomadic peoples of Arabia, / for whom seasonal changes were less significant, / the lunar calendar was a more sensible choice.

That did not make it inevitable / that Islam would use a lunar calendar / and Roman Christianity a solar one, / but political and religious decisions were made / from options limited by geography and lifestyle, / filtered through tradition.