The authors refer to the 'beaching season', and it is with us. A towel hits the sand, we go horizontal, we roast for two weeks. As self-confessed beach bums, Lena Lencek and Gideon Bosker pay homage to the ritual; as academics, their account is keenly researched and tightly chronological – with its roots in mythology, history and sociology.

But geology first. What do we actually put our towels on? A grain of sand is a million years old, it measures a sixteenth of a millimetre and has a pillow-shaped centre. Yellows, pinks, purples, reds, blacks make up the mix – depending on location and the substance eroded. Some are alabaster smooth, some jagged. And when these grains scrape, they 'sing': silky rustles come off the dunes of Hawaii, the sands at Oregon emit high-pitched squeaks, the beaches of Jebel Nagous groan in the wind.

The Romans were quick to exploit the yellow stuff, breaking a multitude of superstitions that linked the shore with malign spirits. They built fashionable Baiae, which prospered for 500 years. (It still stands as the longest running resort.) Here, a notion of otium was played out: constructive recreation in the form of bathing, boating and barbecues. A sort of 'awayday'