Is it bad to start a sentence with a citation [duplicate]

The junction has a stop sign on each of the four entrances.
The junction has a stop sign on each of the 4 entrances.

The first is preferred, for some reason, by many English texts. Why? I haven't seen this phenomenon in other languages.

I have also noticed when reading French and Spanish texts, that it is quite normal to write numbers below ten in full as well, e.g. "los tres hombres que..." instead of "los 3 hombres que..."

My guess is that writing numbers in full in a European language is easier than using Roman numerals, which were the mainstay until the Arabic-Hindu number system came to Europe. Eg, it is easier to understand "one hundred and fourty five" than it is to understand CVL or CXLV or CXXXXV, which are all different and valid ways of writing 145, with CXXXXV being the most common. Clumsy. So after the vastly superior Hindu-Arabic system was adopted in Europe, the habit of writing numbers as words would have remained.

English, being a European language, would have kept similar habits as per the other European languages.

Today, it is a simply an issue of style, so it is not wrong to always write numbers with numerals or to always write them in full. For instance, APA recommends that numbers below 10 are written in full, while numbers 10 and above are written with numerals. The Chicago Manual of Style recommends that all numbers below 100 are written in full, with numbers above 100 written as numerals.

Both style guides prohibit mixing spelt out numbers with numbers expressed as numerals, favouring numerals for all numbers when they are mixed. But my local newspaper, quite happily mixes numbers 1-9 spelt out, and higher numbers expressed with numerals.

The rules in both style guides (and others) are actually a lot more comprehensive than that, but I see no reason to include them here.

Most high schools teach similar rules in their English classes, which leads to everybody being accustomed to writing numbers out in full. In addition, as everybody is used to seeing numbers expressed like that in their novels, newspapers, and other texts, it becomes further engrained in the psyche of English writers.

I had the impression that while it does boil down to a matter of style, the rule of thumb was "if you are writing words (i.e. English prose), use the word form, and if you are writing numbers (i.e. math) use the numerals", until the word form becomes so large as to become cumbersome.

Generally, numbers up to twenty are written as a word, because it is just one word. Go any further than twenty and you are dealing with compound words, which I guess people don't like very much. So numbers greater than twenty are written as numerals.