There are various pictures pre-dating the 1967 Six Day War, available on the Internet and in various scholarly sources, clearly showing free mixing among the genders at the Kotel (Western Wall) in the midst of prayers without any mechitza. (It's possible that they never had any formal minyanim there, but that seems unlikely). Are there any halachic authorities which relate to these practices at the Kotel?
A large collection of pictures can be found at The National Library of Israel - 150 Years of Photographs of the Kotel
Here's are some examples: