Hmmm ... somehow I hae me doots about the origins of the tilde as presented in the Calcutta Telegraph:

I am a fan of Amitav Ghosh. He chooses such exotic subjects. Like the great romantic novelists, he takes us to explore the unknown and the strange. He is my Indian Conrad. I am not sure that I have read all his novels. But to my knowledge, The Hungry Tide is his first novel about Bengal. He has made even Bengal romantic in this book.

There is another novelty about The Hungry Tide: Amitav uses a tilde, my favourite diacritical mark. It is one of the two features of Portuguese which make it such an attractive language — the other being the Portuguese pronunciation of j as zh — as in leisure. I do not mean the Punjabi pronunciation, which is close to leiyur; I mean the s as in measure, and not the y as in mayor. And Amitav uses the tilde as in bãdh, “a tall embankment”, or Morichjhãpi, or search me.

I was told that this tilde was invented as a labour-saving device by the Romans. They were great ones for laws and documents; and since they did not have personal computers, they had to write out everything in longhand — and copy it any number of times. Apart from the labour of writing, every document had to be written on something. That something was papyrus, the wonder writing base from Egypt, where the papyrus reed grew on the banks of the Nile. Its rind was stripped off, its pith was laid out in strips, another layer of strips was laid on it at a right angle, and the two layers were hammered together into a sheet. It was a laborious process. Egypt had a monopoly on papyrus, and both Greece and Rome had to import it. It made a hole in their trade balances.

Then just before the birth of Christ, Egypt declared an embargo on the export of papyrus. Greek philosophers were in agony: how were they to write epics and drama without papyrus? One philosopher (literally, lover of knowledge) looked around, and inspiration came to him. All around his school, in the shadow of Acropolis, grazed cows and goats. He took the skin of a goat, cleaned it of hair and fat, and stretched it out and dried it. Thus he got parchment — a smooth, durable medium for writing which could be rolled up and shelved. After that, as long as the Greeks ate enough sheep, goats and cows, they could go on writing books without worrying about a shortage of material. If they wanted to write more books, they only had to eat more goats.

The Greeks did many experiments with the preparation of parchment. Some put lime in the water in which the hide was soaked; others put flour and salt. Some put oak gall to tan the hide; others tried out dog shit — a technology the Jews did not take to. But everyone had one suited to his tastes.

Instead of rolling them up into scrolls like the Greeks, the Romans stitched together sheets of parchment like our present-day books; they came to be known as codices. The word comes from caudex, which was a wooden stump to which petty criminals in Roman times were tied like modern cows or goats. This goes back to a time when the Romans wrote on wooden sheets covered with wax — they scratched out the letters on wax with a stylus. It was easier to scratch out straight than curvy lines; so instead of U they wrote V. If you do not believe me, go to Rome and walk around; you will find many triumphal arches the Romans built to bear me out. They wrote Marcvs Avrelivs, for example.

Even though the Greeks and the Romans ate all the animals they could, it was prudent to be economical in the use of parchment. Some people erased what was written on parchment and rewrote on it; such a manuscript, born of parsimony, was called a palimpsest. Many Roman words ended in m and n. They wrote the m or n on top of the vowel before it to save horizontal space. That is how the tilde was invented. After they departed, their descendants used it whenever they wanted to give a word a nasal twang. ...

... I was led to believe the tilde had its origins in manuscripts to indicate a letter was doubled (especially Ns)