Ekkaia, also called the Enfolding Ocean and the Encircling Sea, is a dark sea that surrounds the world before the cataclysm at the end of the Second Age. During this flat-Earth period, Ekkaia flows completely around Arda, which floats on it like a ship on a sea. Above Ekkaia is a layer of atmosphere. Ulmo the Lord of Waters dwells in Ekkaia, underneath Arda. Ekkaia is extremely cold; where its waters meet the waters of the ocean Belegaer on the northwest of Middle-earth, a chasm of ice is formed: the Helcaraxë. Ekkaia cannot support any ships except the boats of Ulmo. The ships of the Númenóreans that tried to sail on it sank, drowning the sailors. The Sun passes through Ekkaia on its way around the world, warming it as it passes.