How did opening doors for women actually get started?

Recently, on a message board I frequent, a topic was started about chivalry(and if it was dead) One person who posted in that thread must be completely against chivalry, because she suggested that the habit of opening doors for women started out in medieval times as a way for *men* to keep from being assassinated... show more Recently, on a message board I frequent, a topic was started about chivalry(and if it was dead) One person who posted in that thread must be completely against chivalry, because she suggested that the habit of opening doors for women started out in medieval times as a way for *men* to keep from being assassinated in doorways by letting women go first!

Somehow I've never heard that little tidbit, so I cry BS.. if there's anyone out there that knows a good place to find out about medieval customs, and the truth about that custom(or even if she's right!) please point them out to me so I can either admit she's right, or point it out to her she's wrong.
Thanks in advance!
Update: Just to add- to those men out there that still open doors for ladies-don't stop, please! There *are* some ladies that still appreciate it more than you know! You guys are awesome! (and thanks to those replying, It's really helping!)
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