These are clearly magical symbols. Unusual symbols, arranged in an unusual manner, asymmetrically, making it hard to make out their intent, even before the sands and winds had taken their due from the stone.
They're also different from the rest of the symbols you have encountered thus far in Telkomel, the work of a different class, or perhaps of a different tradition.
You dig through the many records you have studied, the signs you have learned, the languages known and unknown, coming up with a few ideas for various symbols. Protection. Burnishing. Light. Color. It occurs to you that the stone is unmarred by the sand, that the cuts are clean and the color brilliant, despite the age of the arch. It seems it's a spell to keep the stone beautiful no matter how long it sits in place.
