Isn't that era name read "Tengen"? (This would put the year at about AD 980.)
It is. Seems to have been a simple typo on my part, since "gou" isn't even a possible reading for the kanji. Also, Japanese Wikipedia actually mentions the Rashomon gate being knocked over by a storm that year. While we're on the subject, I really love the wider implications of this story supposedly being set in medieval Japan.
