WHY BRIDGES ARE BUILT IN SECRET
L. Nelson (Legends of Liberia)
Long before white men were known in the land there lived a rich woman by the name of Sagba Massa. Sagba possessed a certain magic ring which she always wore on her hand; with this ring she could summon and control the power of spirits and forest devils, and her clan, whom she rules, prospered accordingly. Her lands yielded abundant crops, rain fell when rain was needed, and evil beings who walked in the night left her people alone.
The Chief of Sagba's tribe, a wise old man called Mana Kpaka, sent messages through the land requiring lesser chiefs and clan leaders to assemble at his town for a converence concerning tribal warfare. Sagba Massa set out on her journey to this town, and on the way she was obliged to cross the Yanjah River. While crossing in a canoe she saw a beautiful woman sitting on a rock, and wondered who she was. A moment later the woman disappeared, and Sagba, whose hand was trailing lightly in the water, suddently felt her magic ring drawn gently from her finger.
She cried out in alarm and peered down into the shining water, but saw nothing there. The beautiful woman who sat on the rock had been a water spirit, and doubtless it was she who had stolen the precious ring. Sagba made camp on the river bank and called up her best diviners to discover what she must do: the diviners read their sands and gave her their advice.
Three men were brought from distant places. One of them had power over water. The second had power over light and could see into the very heart of mountains. The third had power over earth, and could crush the biggest rocks to powder in his hands. Sagba Massa paid them well and commanded them to find her ring.
The first man tipped the river on its side.
The second man saw the ring hidden inside a rock which lay in the river bed.
The third man lifted the rock and broke it, and having found the ring he gave it back to Sagba. She went to the conference called by Mana Kpaka, and when returning she decided to build a bridge across the Yaajah river, a bridge which would nowhere touch the water.
With the aid of her ring a number of spirits were summoned and they were told to build a bridge from bank to bank in such a way that men who crossed might be beyond the reach of mischievous river spirits. The spirits said they would work by night, but men must work by day. Trusted men were called upon to build the bridge by day; and the spirits threw building medicine on them so they would build well and make no error. The spirits selected two large trees on opposite banks, and swung stout lines of cane and vines across the river from tree to tree; but they only worked by night, when no one was about. The men used secret knots and the cunning of their medicine to weave a slender footwalk between the hangling lines; they worked only by day, and no man who was not one of them was permitted to be there.
Thus the first suspension bridge was built, and now the manner of this work is a closely guarded secret handed on from father to son. The secret is known only to spirits and selected groups of men, and anyone who tries to watch is killed.
Strictly speaking this isn't an explanation of why the spirits wanted everything to be secret, but never mind that.
You would think that the people walking over it every day would be able to look at the knots and reverse engineer the method, but I'll bet there are some non-obvious tools involved. Think patent enforcement.
I couldn't figure it out, but I'm no good with visualizing, or successfully tying, any but the simplest knots.