Movie effects in 1963 were unbelievably impressive. Even with all the technological limitations, filmmakers refused to let those limits hold back their imagination.
Why does The Lord of the Rings still look so good?
Many reasons, but here's one: Minas Tirith wasn't CGI. They built a miniature version of the city and filmed that. It looks realistic — because it was real.
And this wasn't even the biggest model they made...