Atually, it's not only the anniversary of Hiroshima. It's also the anniversary of the date that Emperor Romanos IV Diogenes was captured and Islam advanced through Europe. That would have been 1071.
There were also a couple of Jewish massacres on August 5th, back in the middle ages.
The above comes from Brainy History, and thanks to flutters for providing the link awhile back.
Thanks Tilly. I love browsing brainyhistory.com there is always something interesting.