The festivities are supposed to commence when the first person climbs to the top of the two story high, highly greased up wooden pole. However, since this usually takes a while, people just don't wait, and the tomato fight starts early. The fight is part of an annual festival that has taken place for the past 60 years.
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Related Post:
La Tomatina - Tomato Fighting Festival.
Post Title → Tomatina Tomato Fight 2010