Every year near the end of June, residents of the small town of Haro in the Rioja region of Spain rise with the sun in anticipation of a wine-slinging battle that Bacchus himself would be proud of.

Whether waking early or carrying on from the night before, participants, clad in white shirts and red bandanas, follow the mayor and his trusty steed up to the Hermitage of San Felices de Bilibio, which sits at the edge of a cliff. After mass at the holy site, everyone arms themselves with buckets, water pistols, bottles, and sprayers filled with wine, and the whole scene erupts into a messy spree of liquid grapery. Tankers of wine, donated by local winemakers, supply the ammunition, as friends become rivals in the battle to cover every inch of each person in a panoply of purple. There is, of course, plenty of drinking, as some revelers are known to take a few sips mid-battle. Finally, soppy masses of violet bodies travel down the hill to the Plaza de la Paz, where performances and more drinking provide distraction from the sticky, stinky carnage left after battle.

Origins of this messy tradition are unclear. While some say the battle was born out of a territorial dispute between Haro and its neighbor, Miranda De Ebro, others point to pilgrims who visited the San Felices hermitage. As the story goes, one day pilgrims were enjoying a wine-filled lunch after mass at the hermitage when it spontaneously erupted into mirthful wine-slinging shenanigans. No matter how it began, this fun-filled spectacle celebrates the renowned wine-producing region, so taking a tipple or two before, during, or after the event is highly encouraged.

If you’re a visitor, good luck outwitting a local: Even the most wily interloper is unlikely to pose a sufficient threat to residents who have been honing their tactics for years. Your dry days are likely numbered.