Great Mourning is the name of the stone on which they placed the Ark of the Covenant when it was returned to Israel by the Philistines.

1 Samuel 6:13. And those of Beit Shemesh were reaping their wheat harvest in the valley, and they lifted up their eyes and saw the Ark and rejoiced to see it. 14. And the cart came into the field of Joshua, a Beit-Shemite, and stood there, where there was a great stone. And they cut the wood of the cart and offered the cows, a burnt offering to the LORD*. 15. And the Levites took down the Ark of the LORD* and the box that was with it, in which were the jewels of gold, and put them on the great stone and the men of Beit Shemesh offered burnt offerings and sacrificed sacrifices the same day to the LORD*. 16. And when the five leaders of the Philistines had seen it, they returned to Ekron the same day.