OpenGL GL_TRIANGLES is not working

I am unable to get GL_TRIANGLES to render anything. GL_QUADS and GL_LINES both shows something at least.

   glClearColor(0.35,0.35,0.35,0);
   glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

   glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);

   glBegin (GL_TRIANGLES);


   for(int i = 0; i < face.size(); i++) {
      unsigned int index1 = face[i].first_V-1;
      unsigned int index2 = face[i].second_V-1;
      unsigned int index3 = face[i].third_V-1;

      glNormal3f(norm[index1].x, norm[index1].y, norm[index1].z);
      glVertex3f(vert[index1].x, vert[index1].y, vert[index1].z); 

      glNormal3f(norm[index2].x, norm[index2].y, norm[index2].z);
      glVertex3f(vert[index2].x, vert[index2].y, vert[index2].z);

      glNormal3f(norm[index3].x, norm[index3].y, norm[index3].z);
      glVertex3f(vert[index3].x, vert[index3].y, vert[index3].z);

   }

   glEnd();
   glutSwapBuffers();