<P> The quality of the rock in the Valley is inconsistent, ranging from finely - grained to coarse stone, the latter with the potential to be structurally unsound . The occasional layer of shale also caused construction and conservation difficulties, as this rock expands in the presence of water, forcing apart the stone surrounding it . It is thought that some tombs were altered in shape and size depending on the types of rock the builders encountered . </P> <P> Builders took advantage of available geological features when constructing the tombs . Some tombs were quarried out of existing limestone clefts, others behind slopes of scree, or were at the edge of rock spurs created by ancient flood channels . </P> <P> The problems of tomb construction can be seen with tombs of Ramesses III and his father Setnakhte . Setnakhte started to excavate KV11 but broke into the tomb of Amenmesse, so construction was abandoned and he instead usurped the tomb of Twosret, KV14 . When looking for a tomb, Ramesses III extended the partly - excavated tomb started by his father . The tomb of Ramesses II returned to an early style, with a bent axis, probably due to the quality of the rock being excavated (following the Esna shale). </P> <P> Between 1998 and 2002 the Amarna Royal Tombs Project investigated the valley floor using ground - penetrating radar and found that, below the modern surface, the Valley's cliffs descend beneath the scree in a series of abrupt, natural "shelves", arranged one below the other, descending several metres down to the bedrock in the valley floor . </P>

How many pyramids are there in the valley of the kings