Celebration of this day as one of the 2 happiest days of the year, with Yom Kippur: Taanit 26b
On the 15th of Av, after the Jews entered Israel, permission was granted for the 12 Tribes to marry each other: Taanit 30b
On the 15th of Av, permission was granted for the tribe of Binyamin to marry other tribes, after the tragedy of The Concubine in Giv'ah: Taanit 30b
On the 15th of Av, the people dying for the Sin with the Spies stopped dying: Taanit 30b
On the 15th of Av, Hoshe'a ben Aylah destroyed the roadblocks which Yeravam ben Nevat had erected to keep people from ascending to the Temple: Taanit 30b
On the 15th of Av, permission was granted for the Jews to bury the dead of the Betar rebellion: Taanit 31a
On the 15th of Av, they completed chopping wood for the Temple Altar: Taanit 31a
How the 15th was Celebrated, Historically
Custom of the single girls to dress in white clothing when going out to find husbands, all of them borrowing the clothing to prevent embarrassment of those who don't have: Taanit 26b, 31a
Which strata of society borrowed clothes from which for this purpose: Taanit 31a
All of the clothing was immersed to prevent embarrassment of girls who were menstruating: Taanit 31a
The girls telling their virtues to the single men, in an attempt to attract them for marriage: Taanit 26b, 31a