Lethe
In Greek mythology, Lethe (; Ancient Greek: "Lḗthē"; , ), also referred to as Lemosyne, was one of the five rivers of the underworld of Hades. Also known as the "Ameles potamos" (river of unmindfulness), the Lethe flowed around the cave of Hypnos and through the Underworld where all those who drank from it experienced complete forgetfulness. Lethe was also the name of the Greek spirit of forgetfulness and oblivion, with whom the river was often identified. In Classical Greek, the word "lethe" (λήθη) literally means "oblivion", "forgetfulness", or "concealment". It is related to the Greek word for "truth", "aletheia" (ἀλήθεια), which  through the privative alpha literally means "un-forgetfulness" or "un-concealment". Infernal river. Lethe, the river of forgetfulness, is one of the five rivers of the Greek underworld; the other four are Acheron (the river of sorrow), Cocytus (the river of lamentation), Phlegethon (the river of fire) and Styx (the river that separates Earth and the Underworld). According to Statius, it bordered Elysium, the final resting place of the virtuous. Ovid wrote that the river flowed through the cave of Hypnos, god of sleep, where its murmuring would induce drowsiness. The shades of the dead were required to drink the  waters of the Lethe in order to forget their earthly life. In the "Aeneid" (VI.703-751), Virgil writes that it is only when the dead have had their memories erased by the Lethe that they may be reincarnated. The river Lethe was said to be located next to Hades' palace in the underworld under a cypress tree. Orpheus would give some shades (the greek term for ghosts or spirits) a password to tell Hades' servants which would allow them to drink instead from the Mnemosyne (the pool of memory), which was located under a poplar tree. An Orphic inscription, said  to be dated from between the second and third century B.C. warns readers to avoid the Lethe and to seek the Mnemosyne instead. Drinkers of the Lethe's water would not be quenched of their thirst, often causing them to drink more than necessary. Goddess. Lethe was also the name of the personification of forgetfulness and oblivion, with whom the river was often associated. Family. Hesiod's account. Although some sources have mistakenly identified Lethe as the daughter of Oceanus, the father of other river goddesses, Hesiod's "Theogony" identifies her as the daughter of Eris ("strife"), and the sister  of Ponos ("Hardship"), Limos ("Starvation"), Algea ("Pains"), Hysminai ("Battles"), Makhai ("Wars"), Phonoi ("Murders"), Androktasiai ("Manslaughters"), Neikea ("Quarrels"), Pseudea ("Lies"), Logoi ("Stories"), Amphillogiai ("Disputes"), Dysnomia ("Lawlessness"), Ate ("Ruin"), and Horkos ("Oath"). Hyginus' account. In another account, Aergia was called the daughter of the primordial deities Aether and Gaia. Mythology. According to Statius, Lethe was said to be the "dull" guard in the court of Hypnos (Sleep) in the Underworld. Lethe is often compared to Mnemosyne, the goddess of memory. Roger Brooke describes their dynamic in his 1999 book "Pathways into the Jungian World: Phenomenology and Analytical Psychology" stating "Rather than only  constituting disaster and darkness, Lethe also presents their obliteration – something like the withdrawal of life...". Role in religion and philosophy. Some ancient Greeks believed that souls were made to drink from the river before being reincarnated, so that they would not remember their past lives. The Myth of Er in Book X of Plato's "Republic" tells of the dead arriving at a barren waste called the "plain of Lethe", through which the river "Ameles" ("careless") runs. "Of this they were all obliged to drink a certain quantity," Plato wrote, "and those who were not saved by wisdom drank more  than was necessary; and each one as he drank forgot all things." A few mystery religions taught the existence of another river, the Mnemosyne; those who drank from the Mnemosyne would remember everything and attain omniscience. Initiates were taught that they would receive a choice of rivers to drink from after death, and to drink from Mnemosyne instead of Lethe. These two rivers are attested in several verse inscriptions on gold plates dating to the 4th century BC and onward, found at Thurii in Southern Italy and elsewhere throughout the Greek world. There were rivers of Lethe and Mnemosyne at  the oracular shrine of Trophonius in Boeotia, from which worshippers would drink before making oracular consultations with the god. More recently, Martin Heidegger used "lēthē" to symbolize not only the "concealment of Being" or "forgetting of Being", but also the "concealment of concealment", which he saw as a major problem of modern philosophy. Examples are found in his books on Nietzsche (Vol 1, p. 194) and on Parmenides. Philosophers since, such as William J. Richardson have expanded on this school of thought. The goddess Lethe has been compared to the goddess Meng Po of Chinese Mythology, who would wait on  the Bridge of Forgetfulness to serve dead souls soup which would erase their memories before they were reincarnated. Real rivers. Amongst authors in antiquity, the tiny Lima river between Norte Region, Portugal, and Galicia, Spain, was said to have the same properties of memory loss as the legendary Lethe River, being mistaken for it. In 138 BCE, the Roman general Decimus Junius Brutus Callaicus sought to dispose of the myth, as it impeded his military campaigns in the area. He was said to have personally crossed the Lima, and then called his soldiers from the other side, one by one , by name. The soldiers, astonished that their general remembered their names, crossed the river as well without fear. This act proved that the Lima was not as dangerous as the local myths described. In Cádiz, Spain, the river Guadalete was originally named "Lethe" by local Greek and Phoenician colonists who, about to go to war, solved instead their differences by diplomacy and named the river Lethe to forever forget their former differences. When the Arabs conquered the region much later, their name for the river became Guadalete from the Arabic phrase "وادي لكة" (Wadi lakath) meaning "River of Forgetfulness". In  Alaska, a river which runs through the Valley of Ten Thousand Smokes is called the River Lethe. It is located within the Katmai National Park and Preserve in southwest Alaska.