Dodecanese relative quiet and prosperity. In 408 BC, the three cities of Rhodes had united to form one state, which built a new capital on the northern end of the island, also named "Rhodes"; this united Rhodes was to dominate the region for the coming millennia. Other islands in the Dodecanese also developed into significant economic and cultural centers; most notably, Kos served as the site of the school of medicine founded by Hippocrates. However, the Peloponnesian War had so weakened the entire Greek civilization's military strength that it lay open to invasion. In 357 BC, the islands were conquered by
Island of the Jewel Island of the Jewel The Island of the Jewel () or Island of Sapphires () was a semi-legendary island in medieval Arabic cartography, said to lie in the Sea of Darkness near the equator, forming the eastern limit of the inhabited world. The island does not appear in any surviving manuscript of Ptolemy's "Geography" nor other Greek geographers. Instead, it is first attested in the Ptolemaic-influenced "Book of the Description of the Earth" compiled by al-Khwārizmī around 833. Ptolemy's map ended at 180° E. of the Fortunate Isles without being able to explain what might lay on the imagined eastern