In her new book “The Far-Farers: A Journey From Viking Iceland to Crusader Jerusalem,” former British journalist Victoria Clark draws thoughtful and subtle parallels between the beginning of the first millennium and the second. This account, an engaging blend of journalism and history, shows how the 11th century’s militant Christianity laid the groundwork for the later separation of church and state in Western Europe. It also shows how the crusaders’ anti-Semitism and demonization of Islam still haunt us today.

Clark retraces the steps of a young Viking, Thorvald the Far-Farer, who, having failed to convert Iceland to Christianity, went into exile, setting sail for the Holy Land in 986. Following Thorvald’s path–and then that of the 11th-century crusaders–she crosses Germany, Poland, France, Italy, Albania, Greece, Turkey and the Middle East. “The Far-Farers” recounts her journey, interspersing colorful historical flashbacks with bits of modern reportage. By traversing 10 countries and 1,000 years of history, Clark seeks to illustrate the lasting repercussions of mixing religion with politics.

What she finds is an increasingly pervasive secularism. Centuries of religious strife and two world wars, she writes, have left most Europeans bound not by faith but by trade, finance and human rights. Such secularism makes the few religious visionaries she encounters that much more striking. In Poland she meets with Archbishop Muszynski of Gniezno, who tells her–echoing Otto III’s grand scheme of a thousand years ago–that what his country has to offer the EU is a new Christian spirituality to complement its economic ties.

Clark reminds us just how dangerous such a view can be. She recalls how, upon reaching Jerusalem in 1099, the crusaders conducted an orgy of slaughter against Arabs and Jews, convincing the Arabs that the only way to survive was to revive the jihad. Modern events, too, intervened to prove Clark’s point: she wrote the last lines of “The Far-Farers” just weeks after Islamic fundamentalists flew planes into New York’s World Trade Center, prompting U.S. President George W. Bush to call for a “crusade” against terror. The word was quickly retracted. But this timely account highlights the disturbing parallels that remain.