Hanging clothes on a line between concrete pillars without drilling
Wrap one end of the rope around a pillar 3-4 times, tie the loose end back to the standing portion of the rope (probably with a bowline), and then slide the wraps up to the top of the pillar so that the part furthest from the knot is highest, with the rope smoothly wrapping down from that point. Do the same for the other end, tightening the rope enough to get it as far off the ground as you like (use another bowline, or a taut-line hitch, whichever is more convenient).

The friction between the rope and the pillar will increase exponentially with the number of wraps of contact; 3-4 wraps and a relatively rough pillar will make it impossible to drag the rope down.