The 17th of Tammuz is an infamous day in Jewish history. After forty days on Mt. Sinai, Moses leaves the presence of God and descends to the Hebrew people. He sees the people worshipping the golden calf, gets really angry and throws down the tablets which break into pieces. On this day in 586 BC the Babylonians and in 70 AD the Romans breached the walls of Jerusalem. Three weeks afterward, the city and Jewish temple were destroyed.
Moses turned, and went down from the mount, and the two tables of the testimony were in his hand: the tables were written on both their sides. And it came to pass, as soon as he came nigh unto the camp, that he saw the calf, and the dancing: and Moses' anger waxed hot, and he cast the tables out of his hands, and brake them beneath the mount (Exodus 32:15, 19-20).