Zechariah 8 - The fast of the 4th; 5th, 7th and 10th months. Four fast days commemorate what?

Zec 8:18
Then the word of the LORD of hosts came to me saying,

Zec 8:19
"Thus says the LORD of hosts, 'The fast of the fourth, the fast of the fifth, the fast of the seventh, and the fast of the tenth months will become joy, gladness, and cheerful feasts for the house of Judah; so love truth and peace.'

The four fast days commemorate: (1) the siege of Jerusalem , (2) the breaching of the walls of Jerusalem, (3) the destruction of the temple and Jerusalem, and (4) the murder of Gedaliah. This mourning was to turn to rejoicing. They are to love Truth and peace.

River Valley Torah Assembly