Poros stone
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Poros stone is a lightweight, soft, marly limestone that was widely used in construction and statues of Ancient Greece.[1] There is no precise definition of the term, although its roots go to antiquity,[2] when it was used to designate any porous building rock,[3] regardless of its origin,[4] mostly in contrast with marble. In the 20th century the archeologists continued to use the term in the similarly loose way: "poros [was] made to include almost all light-coloured stones" that were not definitely marble or hard limestone.[3]
The poros stone is one of the chief formations of the Neogene (Miocene or Pliocene) in Greece and it occurs at many places in the Peloponnese, making poros a common construction stone there.[2]
Even when hardened by exposure to the elements, poros is much more readily cut with a knife than an ordinary limestone. The ease of working with poros is the reason for its extensive use as a building stone, especially for foundations and other architectonic parts that are not exposed to view.[2]
The Greek geographer Pausanias uses the term "poros" to describe the material of the Temple of Zeus at Olympia, which was built of local shell limestone, Theophrastus (and Pliny the Elder, who borrows the description) declares it to be a less dense variant of Parian marble. Herodotus also contrasts coarse poros with fine marble.[5]