Shivah Asar B’Tammuz

The fast commemorates five tragic events in Jewish history:

1. Moses breaking the tablets at Mount Sinai in response to witnessing the sin of the Golden Calf
2. The ceasing of the daily offerings in the First Temple as a result of the siege of Jerusalem
3. The breaching of the walls of Jerusalem after a lengthy siege, prior to the destruction of the Second Temple
4. The burning of a Torah scroll by Roman General Apostamos 
5. The placement of an idol in the Temple. 

This day begins a three-week mourning period over the fall of Jerusalem that culminates in the fast of the Ninth of Av.