multiple definition exception in cpp

I am starting to learn C++ and am getting this compilation error from my IDE (CodeBlocks). I don't understand why this is happening.

|2|multiple definition of `parser::parseFile()' |2|first defined here|

I don't see how this could happen. This is my entire code base.

main.cpp

#include "parser/parser.cpp"

int main()
{
    return 0;
}

parser/parser.cpp

namespace parser {
    void parseFile() {

    }
}