They raped and pillaged their way across Europe. But Viking warriors were sexually insecure, consumed with performance angst and troubled by the thought that size really did matter.

Being hung like a Norse was key to social hierarchy and being considered a real man in 10th-century Icelandic society, according to a new paper, 'Size Matters: Penile Problems in Sagas of Icelanders', to be presented to the International Medieval Congress in Leeds this week.

The comprehensive cultural history of the penis in medieval Iceland was researched by Dr Carl Phelpstead from Cardiff University, who analysed contemporaneous accounts of otherwise brave Viking warriors being ridiculed by women and girls for their dainty manhood and sexual timidity. 'For Viking men who suffered impotence or erectile problems, it was not merely a medical problem or an unfortunate constraint on their sex lives, it profoundly affected their identity,' said Phelpstead.

Society in medieval Iceland operated under a one-gender system in which people were categorised not as male or female but as physically adequate or inadequate, Phelpstead believes. 'The result is a distinction between men on the one hand and everyone else, including most women, children, slaves and otherwise disenfranchised men on the other,' he said.

In the ancient stories, penis size determined a man's status in a society that distinguished able-bodied, virile men from all other people. In rare cases, some women were able to gain this position of social status. Phelpstead points to repeated imagery and metaphors in the stories that referred to a penis as a 'borer' and 'drill of the hill of the leg'.

'These descriptions suggest that the penis not only marked social position but could be used to establish or reassert social standing through phallic aggression,' he said. 'A penile problem such as erectile dysfunction compromised the ability of a man to assert or maintain this dominant position.'

Phelpstead found evidence for his argument across all genres of Old Norse-Icelandic literature, as well as a cult of the phallus in pre-Christian Scandinavia, including ithyphallic rock carvings from Stone Age Norway and Bronze Age Sweden. He also identified castration anxiety among Viking men caused, he believes, by laws in force until 1260 allowing it as a kind of contraception and social engineering.

According to Phelpstead, having a penis was of less significance than whether its possessor had sufficient virility to produce an erection. 'Erectile dysfunction was both a symptom and a sign of men's move from one side of the social binary to the other,' said Phelpstead. 'If they were no longer vigorous men, they lost their gendered identity altogether.'

To complicate matters further, Phelpstead found evidence in the stories that it was as unmanly to have an outsized penis as an undersized one. In the 13th-century Njal's Saga, the warrior Hrutr Herjolfsson is cursed by a jealous queen with an erection too big for intercourse with his bride.