I am interested in the history of how numbers were spoken with respect to hundreds, tens, unities... (or more generally powers of a base if the systems is not decimal). To clarify, here is an example: in English, we say twenty one and, accordingly, write it 21, but there seems to be an older structure in numbers like sixteen, which we write 16 for mathematical consistency, but speak in the opposite order: 'six and ten'. Since this happens only for small numbers (less than twenty), I think it may be the way numbers were originally spoken and after the introduction of numerical systems the way bigger numbers were spoken was inverted. Also, since the positional number system as we use today comes from Arabic (an ultimately from Hindu) and they write in the opposite direction, I would also like to know how they speak their numbers, if they say the unities before and tens last, or the other way around, as in English or Portuguese.
An example of how the spoken numerals influenced the way they were written numerically is the Slavic languages and their Cyrillic alphabet. Since Cyrillic is derived from the Greek alphabet, it also inherited the Greek tradition of writing numbers with letters, isopsephy (gematria), which dates back to Euclid, about 300 BC. The first 9 letters were assigned the numeric values of 1 to 9, the next 9 letters meant tens, 10 – 90, the next nine letters meant hundreds, 100 – 900. 9 × 3 = 27, but the Greek alphabet had only 24 letters, so 3 old letters which had already been abandoned for writing words were kept to be used when writing numerals with letters. The principle was simple: the higher orders first, so, for example, 666 was written as χξϛ (600 + 60 + 6). Also, a horizontal line was drawn above the letters used as numbers to tell them from letters used in their usual way to mean sounds. Unfortunately, I cannot reproduce the horizontal line on this site, but in the above link Wiki shows the way it looked like:
The Slavic languages have more phonemes than Greek, the original Cyrillic alphabet had 43 letters, so all the orders had their corresponding letters, 16 letters remained without any numeric value ascribed. The Cyrillic numbers had a special diacritic above them called титло (titlo) which descends from the Greek horizontal line over the numerical letters:
In the Slavic languages of the 9th century AD when Cyrillic appeared and all the way until now the numbers from 11 to 19 are formed according to the model “n + on ten”: modern Russian for 11 is одиннадцать (один-на-дцать) “one on ten”, 13 is тринадцать (три-на-дцать) “three on ten”, etc. As you can see, the principle is practically the same as in English with the numerals 13 to 19, that is, a lower order followed by a higher one, which goes against the Greek tradition of writing the higher orders first. Although in the Greek language numerals 11 to 19 are also formed as n + ten, Greeks wrote the corresponding number according to the numerical logic, 10 + n, e. g. 11 was ια, 10 + 1. The Slavs, however, did not agree with that obvious contradiction of mathematical logic versus natural language, and since the earliest times and all the way until now (in church books and in linguistic research papers) whenever a number from 11 to 19 is written in letters, in Cyrillic it is “n + 10”: