Tucson will celebrate its 239th birthday with a bang tonight at Presidio San Agustín del Tucson.

Cannon fire, along with other festivities, will commemorate the letter Hugo O’Conor penned to Spain on Aug. 20, 1775, identifying Tucson as the spot for a new presidio. It was previously located in Tubac.

“The Presidio (San Agustín del Tucson) is a re-creation of the presidio that was a result of the letter from Hugo O’Conor,” said Marty McCune, a member of the Tucson-Pima County Historical Commission, which began the birthday celebrations in 1975. “Having people dressed up in the costumes gives citizens an element of, ‘Gee, this is really important.’”

A reading of the letter in Spanish and English, mariachi music and a procession of flags from Tucson’s history will highlight a diverse heritage. The event will include the flags of Spain, Mexico, the state of Arizona, the Confederate States of America and the 28-star U.S. flag brought through by the Mormon Battalion. The Davis-Monthan Air Force Base Honor Guard with present the U.S. flag, and representatives from the Tohono O’odham Nation and Pascua Yaqui Tribe will also carry their flags.

Community leaders will sign a proclamation for Tucson’s 239th birthday, but cake makes it official.

Contact reporter Johanna Willett at jwillett@tucson.com or 573-4357. On Twitter: @JohannaWillett