Mandela's personal security arrangements are handled by the South African Secret Service, according to officials at the South African embassy in Washington, D.C.

In addition, as the visit to the United States is designated a "state visit," Mandela is entitled to protection from members of the State Department's Diplomatic Security division.

Cambridge police officers will assist the multi-agency team by controlling access to roads around the Yard.

Outdoor events involving "protectees" or "principals," as they're known in the agency vernacular, post special problems for security agents.

If previous events can be any indication, expect under-cover agents wandering through the crowds, and observer (and possibly sniper) teams on nearby roof-tops.

There's no word whether Mandela will receive a contingent of U.S. Army Delta Force commandos, ready and waiting to spring into action, as several other dignitaries have.

Such a team, according to published reports, usually accompanies the presidential motorcade wherever it travels, and teams have previously been ordered for several high-profile security operations involving foreign dignitaries.

For other visits by heads of state, students seated in the specially designated areas had to pass through magnetometers and be wanded by super-scanners.

But Riley says that no such devices will be used for Mandela's visit.

Controversial Chinese President Jiang Zemin's visit to Harvard Cambridge last November saw exceptionally tight security, on a scale usually reserved for U.S. presidents.

He traveled in armor-plated limousines, trailed by phalanxes of Chevrolet Suburbans carrying security agents from both China and the United States. A police helicopter monitored the motorcade route from above.

Bomb-sniffing dogs searched out every area of Sanders Theatre and before the Chinese president's speech. And Secret Service agents mingled amongst the audience and with the protestors outside.

Although Mandela's tenure as president of South Africa has been controversial, event organizers said they don't expect protesters during his visit.

"We have had no calls as far as protests go," Riley said. "It is...more of a feel-good visit."