The Wikipedia article on letter case says this without citing any references:
Both majuscule and minuscule letters existed, but the difference between the two variants was initially stylistic rather than orthographic and the writing system was still basically unicameral: a given handwritten document could use either one style or the other but these were not mixed. European languages, except for Ancient Greek and Latin, did not make the case distinction before about 1300.
When was the first bicameral script developed, in the sense of using different cases to mark important words or the beginning of sentences (and not just a stylistic choice for the whole document)? And is it true that after bicameral scripts were developed for Greek and Latin, it was only from 1300 that bicameral writing became common for other languages?