Prime Minister Cameron has rejected the proposal that the age of sexual consent be reduced from 16 to 15, arguing that it was needed to ‘protect children’. In the ancient world, there was no such notion. Girls were to be protected from rape and seduction, but that was because they were destined for marriage, whose purpose was the production of legitimate children. It was fertility that was important, not age.

For ancient Greeks, women were reckoned to become fertile at 14. The theory was that in a woman blood and fertility were linked and, by that age, a woman had collected enough blood in her body to have children. If that did not evidence itself in menstruation, sexual activity would bring about the desired result. Some therefore argued that girls should marry at that age.

Aristotle took a different view: because a woman could conceive, it did not follow that she should, and he argued that she would stand a better chance of an easier pregnancy if she waited until she was about 21 (he thought males should hold back as well, believing that semen remained infertile till then). Rather charmingly, he wanted both parties to reach the end of their reproductive cycles together, so suggested that the best age for intercourse was 18 in a girl, 37 in a man. It was Romans who fixed 12 as the age at which a woman could become a legal wife and hold a dowry, and legacies conditional on marriage became payable. It is not possible to determine how frequent such marriages were and whether consummated or not, but the famous educationist Quintilian’s wife was a mother at 13.

What lies at the heart of all this is demographics: the need to maintain a stable, legitimate, citizen population. But giving birth was a life-or-death matter. Only about half of children would reach five. Better start at once, therefore.

Citizenship and legitimacy are no longer seen as central to a secure society; neither, therefore, is marriage or sexual activity in the young. Hence the changing mores and debates in these areas.