Historian Rashid Khalidi's 1997 book "Palestinian Identity: The Construction of Modern National Consciousness" is considered a "foundational text" on the subject. He notes that the archaeological strata that denote the history of Palestine – encompassing the Biblical, Roman, Byzantine, Umayyad, Abbasid, Fatimid, Crusader, Ayyubid, Mamluk and Ottoman periods – form part of the identity of the modern-day Palestinian people, as they have come to understand it over the last century. Noting that Palestinian identity has never been an exclusive one, with "Arabism, religion, and local loyalties" playing an important role, Khalidi cautions against the efforts of some extreme advocates of Palestinian nationalism to "anachronistically" read back into history a nationalist consciousness that is in fact "relatively modern".