The fire was done in this way; nine men would turn their pockets inside out, and see that every piece of money and all metals were off their persons. Then the men went into the nearest woods, and collected sticks of nine different kinds of trees. These were carried to the spot where the fire was to be built. There a circle was cut in the sod, and the sticks were set crosswise. All around the circle the people stood and watched the proceedings. One of the men would then take two bits of oak, and rub them together until a flame was kindled. This was applied to the sticks and soon a large fire was made. 

Sometimes two fires were set up side by side. These fires, whether one or two, were called coelcerth, or bonfire. Round cakes of oatmeal and brown meal were split in four, and placed in a small flour-bag, and everybody present had to pick out a portion. The last bit in the bag fell to the lot of the bag-holder. 

Each person who chanced to pick up a piece of brown-meal cake was compelled to leap three times over the flames, or to run thrice between the two fires, by which means the people thought they were sure of a plentiful harvest. I have also heard my grandfather and father say that in times gone by the people would throw a calf in the fire when there was any disease among the herds. The same would be done with a sheep if there was anything the matter with a flock. I can remember myself seeing cattle being driven between two fires to "stop the disease spreading". 

- Marie Trevelyan, Folk Lore and Folk Tales of Wales, 1909