The main variation in the temples lies in the number of apses found; this may vary to three, four, five or six. If three, they open directly from the central court in a trefoil fashion. In cases of more complex temples, a second axial passage is built, using the same trilithon construction, leading from the first set of apses into another later pair, and either a fifth central or a niche giving the four or five apsial form. In one case, at the Tarxien central temple, the fifth apse or niche is replaced by a further passage, leading to a final pair of apses, making six in all. With the standard temple plan, found in some thirty temples across the islands, there is a certain amount of variation both in the number of apses, and in the overall length—ranging from 6.5m in the Mnajdra east temple to 23m in the six-apsed Tarxien central temple.