Kraken are legendary sea monsters of giant proportions said to dwell off the coasts of Norway and Greenland. The legend may actually have originated from sightings of real giant squid that are variously estimated to grow to 1315 m (4050 ft) in length, including the tentacles. These creatures normally live at great depths, but have been sighted at the surface and have reportedly attacked ships. The sheer size and fearsome appearance attributed to the kraken have made it a common ocean-dwelling monster in various fictional works. The 13th century Old Icelandic saga rvar-Odds saga tells of two massive sea-monsters called Hafgufa ('sea mist') and Lyngbakr ('heather-back'). The hafgufa is believed to be a reference to the kraken: After returning from Greenland, the anonymous author of the Old Norwegian scientific work Konungs skuggsj (circa 1250) described in detail the physical characteristics and feeding behavior of these beasts.