Africa's first mosque stands at Massawa on the Eritrean coast

The first Muslims in Africa landed on the Eritrean coast, and the first mosque on the continent stood at Massawa, possibly built in the 620s or 630s by members of the Prophet's own family. By the tenth century Islam was spreading inland from the Somali coast through the country that is now Somalia, Djibouti, Ethiopia and Eritrea. The usual telling makes the following twelve centuries a straight fight between cross and crescent. Trade reports something quieter. Muslim merchants worked the Christian highlands in numbers and formed a recognised class there known as jiberti, growing wealthy as Red Sea traffic expanded. The Ethiopian state meanwhile cultivated the image of a Christian kingdom besieged in its mountains, a second Israel with the Bible at the centre of its self understanding. The Oromo made Harar a Muslim city of consequence, and its sultanate rose on links to the Funj in Sudan. Sufi orders did the spreading, the Qadiriyya out of Harar into Somalia and Eritrea, the Salihiyya and Ahmadiyya among the Somali.

At Cerrillo, in the west of Puerto Rico, there is a place where people went to work flint. It reads as a workshop rather than a village, since the ground holds the waste of tool manufacture, the flakes and rejected pieces that come off shaping a nodule into something usable. Cerrillo was busiest during the changeover into the Ceramic age, when pottery was being adopted and settlement was reorganising, and the flint had been quarried there before that. The evidence indicates people were taking nodules out of the same deposit back in the Archaic age. That continuity is the interesting part. A source of good stone gets found once and then used for as long as anyone needs stone, across changes in pottery, diet and social arrangement that archaeologists treat as boundaries between cultures. The people at the flint outcrop in the seventh century were going to a place their predecessors had gone to for centuries, for the same reason.