Complex sentence: It was not until late in the 18th century that they came to be considered some sort of writing, when in 1778 Carsten Niebuhr, the Danish mathematician, published accurate copies of three trilingual inscriptions from the ruins at Persepolis.
Split into simpler sentences: It was not until late in the 18th century that they came to be considered some sort of writing. In 1778 Carsten Niebuhr, the Danish mathematician, published accurate copies of three trilingual inscriptions from the ruins at Persepolis.