Before the group declared itself the caliphate reborn that summer, it had been ambiguous about the flag’s meaning and the cause it represented. Was it the flag of an Islamic state, or the flag of the Islamic state—the caliphate that had once ruled land from Spain to Iran and whose prophesied return would herald the end of the world? The Islamic State encouraged the second interpretation but let the global community of jihadists read into the flag and the “state” what they would. The group’s cause proved so compelling among jihadists that in 2014 the organization supplanted its former master, al-Qaeda. The spread of the flag, then, traces the spread of an idea and chronicles a major changing of the guard in the global jihadist movement.

When the Islamic State first announced itself on October 15, 2006, it had no flag of its own. It was not until January 2007 that al-Qaeda’s media distribution arm, al-Fajr, released a picture of the Islamic State’s new flag. Anonymous authors affiliated with the Islamic State explained its design, quoting passages from Islamic scripture and historical accounts. “The flag of the prophet, peace and blessings be upon him, is a black square made of striped wool,” according to one account. Another describes Mohammed “standing on the pulpit preaching” surrounded by fluttering black flags. “On the flag of the prophet was written, ‘No god but God, and Mohammed is the Messenger of God.’” The flag even had a name: “the eagle.”

Although the authors acknowledged other reports of green, white, and yellow flags, they concluded the Islamic State’s flag would be black, because most of the reports about Mohammed mentioned a black flag. The authors were equally confident when explaining the banner’s text. “What is written on the flag is what is written on the flag of the Messenger of God, peace and blessings be upon him.”

The Islamic State’s design of the Muslim profession of faith is different from every other attempt to replicate the prophet’s flag: “No god but God” is scrawled in white across the top and “Mohammed is the Messenger of God” is stacked in black inside a white circle. As the anonymous authors noted, they took the circle’s design from a seal of the prophet used on a set of letters, now housed in Turkey’s Topkapi Palace, that were supposedly written on Mohammed’s behalf. (Modern scholars doubt the letters’ authenticity.) We are meant to believe the Islamic State had inherited the prophet’s seal, just as the early caliphs had.

Why make a flag? In addition to following the prophet’s example, the Islamic State wanted a symbol to rally people to its cause. The group quoted a 19th-century Ottoman historian and official, Ahmad Cevdet Pasha, to make the point:

The secret in creating a flag is that it gathers people under a single banner to unify them, meaning that this flag is a sign of the coming together of their words and a proof of the unity of their hearts. They are like a single body and what knits them together is stronger than the bond of blood relatives.

Yet the Islamic State’s choices display the modern sensibilities they try so hard to displace. The white scrawl across the top, “No god but God,” is deliberately ragged, meant to suggest an era before the precision of Photoshop, even though the flag was designed on a computer. Even the Islamic State’s quotation of Ahmad Cevdet Pasha unwittingly betrays a modern perspective. Influenced by European notions of nationalism yet desiring to hold together the multiethnic Ottoman Empire under sovereign Turkish rule, Cevdet Pasha imagined Islam and its symbols to be the glue. “The only thing uniting Arab, Kurd, Albanian, and Bosnian is the unity of Islam,” he said, according to Dominic Lieven’s book Empire: The Russian Empire and its Rivals. “Yet the real strength of the Sublime State lies with the Turks.”