Błąd kompilacji: "Multiple definition of .."

#include "modules/Game.hpp"
#include "modules/Menu.hpp"

int main()
{
    Game * game = new Game;
    Menu menu( "smallee" );
    while( game->mainWindow.isOpen() )
    {
        sf::Event event;
        while( game->mainWindow.pollEvent( event ) )
        {
            if( event.type == sf::Event::Closed ||( event.type == sf::Event::KeyPressed && event.key.code == sf::Keyboard::Escape ) )
            {
                game->mainWindow.close();
            }
        }
       
        game->mainWindow.clear();
        menu.draw( game->mainWindow );
        game->mainWindow.display();
    }
    delete game;
    return 0;
}