On the 15th of Av 7 things happened to the Jewish people.
1) On these days the daughters of Jerusalem would go out... and dance in the vineyards.
2) The dying of the generation of the Exodus ceased.
3) The tribes of Israel were permitted to marry each other
4) The tribe of Benjamin was permitted to re-enter the community.
5) Hoshea ben Elah opened the roads to Jerusalem.
6) The dead of Betar were allowed to be buried.
7) When the Holy Temple stood in Jerusalem, the annual cutting of firewood for the altar was concluded on the 15th of Av.