72x would be a real challenge, for the little ones !
So the giant would stand 131 meters tall, if we were the little ones.. That is big, a building 40 stories high, just below halfway the Eiffel Tower.. I wonder if medieval weapons would have any effect. His feet would be the size of a house, that is 13 meters long, say 4-5 meters high. Humans with swords could scratch and it a bit, before getting crunched under it.. the giant will feel pain, but he'll stand too large for us to hit the eye with an arrow.
Numbers ? A crowd of 20,000 armed Mongol warriors crawling up the giant's trousers may become quite inconvenient, but I wonder if they'd reach the head. The giant would shed them off.
Changed perspective: suppose we would be the giant
Another way to look at this: the average human is 5-7 feet, divided by 72 you'd get a bipedal creature about 2.5 centimeters high, that is supposed to attack and kill a human. How many would be needed.. now let's suppose a worst case scenario, these medieval little bastards would bring in knives (2.5 millimeter long), arrows (5mm) swords (8mm) and spears (25mm). You would get painful feet, but these little ones cannot kill a standing human with such weaponry. They would have trouble penetrating our skin.
A tree would be handy.. close range cross bow shot while the giant is asleep..
Suppose a medieval army of these 2.5cm soldiers could jump on top of your head, or approach your face, while you are sleeping. A spear of 1.5cm in the eye would be nasty, two of these could render you blind. A crossbow arrow can cause serious trouble. Of course you could wake up and shed them off, but I wonder what would happen if they would be able to penetrate deeper, through the eyes, or through the nose and ears..
In nature, that's the usual way little ones protect themselves, or weak predators kill prey. The little ones could harvest some poison from the Eastern brown snake, and (only !) one of the little ones would attack you, using several arrows with the snake venom. This venom is 8,000 times stronger than cyanide and can kill a human in about one hour.