Al-Jallad began pulling up every inscription that mentioned migrating in search of rain, and soon he had a long list of terms that had resisted translation. Comparing them with the Greek, Aramaic, and Babylonian zodiacs, he started making connections. Dhakar matched up nicely with dikra, the Aramaic word for Aries, and Amet was derived from an Arabic verb meaning “to measure or compute quantity”—a good bet for the scales of Libra. Hunting for Capricorn, the goat-fish constellation, Al-Jallad found the word ya’mur in Edward Lane’s “Arabic-English Lexicon,” whose translation read, “A certain beast of the sea, or . . . a kind of mountain-goat.” He stayed up all night, sifting the database and checking words against dictionaries of ancient Semitic languages. By morning, he had deciphered a complete, previously unknown Arabian zodiac. “We’d thought that they were place names, and, in a way, they were,” he told me. “They were places in the sky.”

Michael Macdonald amassed a vast collection of photographs of these texts and launched a digital Safaitic database, with the help of Laïla Nehmé, a French archeologist and one of the world’s leading experts on early Arabic inscriptions. “When we started working, Michael’s corpus was all on index cards,” Nehmé recalled. “With the database, you could search for sequences of words across the whole collection, and you could study them statistically. It worked beautifully.”

The inscription on Macdonald’s rock included the name of a person (“Ghayyar’el son of Ghawth”), a narrative, and a prayer. It was the narrative that stood out to Al-Jallad. Reading it aloud, he noted a sequence of words repeated three times, which he suspected was a refrain in a poetic text.