... and then he threw the sword as far into the water as he might; and there came an arm and an hand above the water and met it, and caught it, and so shook it thrice and brandished, and then vanished away the hand with the sword in the water. -Malory

Excalibur

   Swords of heroes and sacred kings were typically forged in the Otherworld and were presented to the hero by an otherworldly woman or taken in adventure from a stone, a tree, or as in Excalibur's case both - the Sword in the Stone and the Lady of the Lake gifting it for a later favor with Arthur taking it from a samite clad hand brandishing the sword from the waters of the lake. On the hero's death, the sword must return to its origin.

"So they rode till they came to a lake, the which was a fair water and broad, and in the midst of the lake Arthur was ware of an arm clothed in white samite, that held a fair sword in that hand. Lo! said Merlin, yonder is that sword that I spake of." - Malory
   Ask anyone today, what is Excalibur and they will tell you that it is Arthur's sword taken from the stone to claim his right as king of all Britain. The stories of the Sword in the Stone and the Lady of the Lake gifting were different aspects of the hero sword woven together by Malory. The Sword in the Stone later failed Arthur in combat and not having the original tales, we can not surmise whether he changed the tale to make his own story work or as the Post Vulgate stories state that it was a different sword.
   In terms of the evolution of the Arthurian legend, stories that mention Arthur owning a sword named Excalibur (or a variant of the name) are older than the story of Excalibur being pulled from the stone. In terms of the legends themselves, Geoffrey of Monmouth tells us that Excalibur, which he calls Caliburn was forged in Avalon. Later French author, whose work is usually called the "Post-Vulgate" changed many of the details of the Arthurian legends. According to the Post-Vulgate, the sword drawn from the stone is not Excalibur, but after this sword broke, Arthur went and got Excalibur from the Lady of the Lake. This is also the first appearance of the scabbard in a story, in older stories Excalibur did not have a special scabbard.
   The Welsh name for Excalibur was Caladvwlch, equating linguistically with Irish Caladbolg, the name of a sword borne by heroes in Irish legend, derived from CALAD (hard) and BOLG (lightning).
   At the supposed time of Arthur's historical existence, there were a limited number of sword types in western Europe. There were several distinct types of long-bladed swords, each with a distinctly different style of furniture (hilt, pommel, etc.). The descriptions of Excalibur fit variations of the spatha, the sword used by the Romans. The typical Roman spatha was short and pointed, intended for close-in fighting and principally for stabbing. Other longer variations were double edged and more rounded at the tip. In accordance with H.R.E. Davidson's excellent book on 'The Sword in Anglo-Saxon England', I believe that Excalibur was probably a pattern welded sword that exhibited a herringbone or curved pattern on each side of the blade. It would have been longer than a traditional spatha to allow for fighting from horseback, double edged, and with a fuller (groove) running most of the length. It also was probably inscribed by the swordsmith.
   Phillips and Keatman in their book, 'King Arthur - The True Story', speculate that the two serpents on the sword of Arthur in the Dream of Rhonabwy are the same design as that of the auxilium unit of the Roman army based at Segontium / Caernarvon. Their source is one of the illustrations to the Notitia Dignitatum of the shield of that unit, which has, according to them, two serpents. They propose that Excalibur was a typical Roman spatha.
   Of course, there is also the possibility of Excalibur being an early Byzantine blade as in some stories where it was the sword of Maxen Vledig. And there is evidence that the Alans who fought all over the Eastern and Western Roman Empires and beyond their borders in the early fifth century, fought from horseback using longswords, not spathas.
   Wayland, the smith of the gods and equivalent of Goibniu or Vulcan, was credited with making many of the great magical weapons and armor of the gods, including Excalibur. The fact that he is associated with the Saxons and was purported to have been brought to Britain by them may provide some of the reasons behind one of the Arthurian legends in which Arthur acquires Excalibur from the Saxons, taking it in battle. This plot was used in a recent story, 'The Kingmaking' by Helen Hollick.
   In one historical document, Excalibur was in the Royal Regalia lost by King John when his treasure wagon overturned at The Wash in 1215, whilst he was attempting to avoid the barons. Because it was regalia, it might have still possessed the original furniture, though possibly gilded and with stones added. A case in point is Joyous Gard, Charlemagne's sword. It was created sometime prior to 770 CE, has the same furniture (though gilded and set with stones), and has been preserved as such because it was official regalia. The sword is currently in the Louvre. But there are several accounts of similar forgeries of Excalibur and other legendary weapons.
   Excalibur shall always be linked with Arthur, whether it awaits his return clasped in the Otherworld and guarded by the lady or lies lost and rusted at the bottom of an English pool. From the Otherworld it was given and to the Otherworld it returned.
   Therefore, said Arthur unto Sir Bedivere, take thou Excalibur, my good sword, and go with it to yonder water side, and when thou comest there I charge thee throw my sword in that water, and come again and tell me what thou there seest. -Malory (In an earlier version, Griflet, not Bedivere, was given the task of flinging Excalibur into the waters after Arthur's last battle. When he saw Arthur's tomb, he became a hermit but died shortly afterwards.)

Excalibur in Malory's le Morte

St Galgano Sword in Stone