One of the reasons people believe this celebration came about is because in the middle ages carpenters needed candles and wood to burn during the winter so that they could work in the dim lighting, in spring they no longer needed the candles and wood because it began to get brighter. They burnt all of their remaining wood and candles in spring to celebrate the spring equinox. Over time and because of the intervention of the church the celebration was moved to coincide with the festival of Saint Joseph because he was the patron saint of carpenters.
In recent times and especially during the 20th century during the spanish civil war the ‘falla’ or monuments were anti-clerical or used to show dissatisfaction with the government.
The ‘falla’ are then burnt on the final day of the las fallas. The first falla is lit at around 10pm, but most neighbourhood falla are burnt closer to midnight. The fire brigade are always on call incase of any fallas(failure).