Goren Aravna Beginning of the Beit Hamikdash
When a plague struck the Jewish people as punishment for the census conducted by their king, a message from G-d was conveyed to David by the Prophet Gad: "Go up and build an altar to G-d on the threshing floor of Aravna the Jebusite." (Shmuel II 24:18)
King David was welcomed by Aravna who offered everything he needed for building and equipping such an altar. But David insisted on purchasing the site and the animals that were sacrificed upon it, bringing an end to the plague.
It was on this purchased site that the Beit Hamikdash was built by David's son. This is one of three sites, say our Sages, whose Jewish ownership cannot be disputed since it was actually purchased.