First, the sword which is the topic of this post was not unearthed. It was forged in 1447 by Osafune Norimitsu and is housed in the Kibitsu shrine in Okayama Prefecture. This particular sword has a nagasa or cutting edge of nearly 7.5' and an overall length of nearly 12'. These greatly oversized swords were made as dedications for temples and shrines as obviously they would be impractical if not impossible to use in battle.
Any sword with a nagasa length greater than 3 shaku or 35.7" is considered an O-dachi or O-katana depending on the style of koshirae it is mounted in.
There were o-dachi (large sword) and no-dachi (field sword) made for battle field use in that 36-48" nagasa range, but they were not commonplace.
This is one with a 43" nagasa and an overall length of 70".
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