In the 1st century CE, Pliny the Elder described the phenomenon in his Naturalis Historia, writing that the swell-battered concrete walls became "a single stone mass, impregnable to the waves and ever. Types of octoechos books. The Great Octoechos (ὅκτώηχος ἡ μεγάλη) or Parakletike contained as well the proper of office hymns for each weekday. The hymns of the books Octoechos and Heirmologion had been collected earlier in a book…