A long time ago, beds were expensive—but there’s more to it than that, reports The Atlantic.

“Even livestock often resided under the same roof, because there was no other structure to put them in, and they generated welcome warmth. Among the lower classes in preindustrial Europe, it was customary for an entire family to sleep in the same bed—typically the costliest item of furniture—if not to ‘pig’ together on a straw pile,” Ekirch says. “Genteel couples, for greater comfort, occasionally slept apart, especially when a spouse was ill.”