Last Saturday, in the Kenyan town of Machakos, representatives of Sudan's northern-based Muslim government joined with a Christian-led southern rebel faction to sign a protocol that could eventually end the country's 19-year civil war. While still short of a full peace accord, the accomplishment is impressive. To reach this détente after a bloody roller-coaster ride of ethnic and religious warfare, Sudan's Muslim rulers have had to back away from a pact supposedly as old as Islam itself.

The Pact of Umar, a document purportedly signed by the second caliph, Umar I (634-44), is the source of the restrictive regulations on non-Muslims embedded in the Shari'ah or Islamic law. In 1983, Sudan's northern Muslim government took a fundamentalist turn and imposed the Shari'ah on the Christian south. This triggered the warfare that has since killed more than 2 million Sudanese and displaced millions more.

Under Shari'ah, both Jewish and Christian minorities (dhimmi, or literally "protected peoples") have freedom to remain in Muslim countries but no freedom to recruit. Conversions can only be to Islam, not away from it.

Like other early and medieval documents with weighty consequences for politics and religion, Umar's pact is hard to pin down to a date. It may have originated as early as 673, after the Muslims conquered Christian Syria and Palestine. But scholars date the text in its current form to about the ninth century.

The pact is purportedly written by the conquered Christians themselves. In it, those Christian subjects gratefully receive the protection of their Muslim masters and in return agree to certain religious and social strictures:

We shall not build, in our cities or in their neighborhood, new monasteries, churches, convents, ...