Why do we use 10 characters to make up the value of 1?

This might seem like a silly question but I was thinking about how we have 10 symbols. By default to express a value between zero and one you have 10 options for characters. This can lead to confusion of 1/3 being expressed as a recurring decimal.

Let's say we used the first 12 letters of the alphabet you could write 1.333333333... as A.D

By using this method of expression could we find further patterns in maths that are easier to see?

Sorry if I'm not making sense I have a basic secondary school understanding of maths. But I'm really wondering why 10 symbols (1234567890)? That idea seems constructed rather than a discovered fact. I'm sure it's because we have 10 fingers and so biologicaly we think in 10s.