Staging a massive civil war battle re-enactment forced the risk manager of Prince William County, Va., to scramble for insurance coverage.

The county in northern Virginia is home to the site where Union and Confederate troops clashed for the first time in 1861 in the First Battle of Bull Run, referred to as First Manassas by the Confederate States Army.

To help host a 150-year anniversary re-enactment in 2011, the county prepared for thousands of people who would participate as soldiers and spectators.

Preparations included more than a year of planning by the Prince William County Police Department. But just three months before the event and with tickets already sold, the county learned that a nonprofit staging the multiday re-enactment couldn't obtain the necessary insurance arrangements.

“So I got thrown into that,” said Lori J. Gray, the county's risk management division chief.

Her challenges included getting information to help her broker, Aon P.L.C., convince a general liability insurer to underwrite coverage for the re-enactment held on private farm land. The underwriters needed to know the number of re-enactment participants expected, how many days they would camp on the property, what their rifles and cannon would fire and so on.

American International Group Inc. eventually wrote the coverage.

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Ms. Gray also considered weather insurance, but she didn't buy it because tickets purchased by spectators were nonrefundable and the county would not be liable for a cancellation.

Her biggest insurance challenge came when the property owner did not understand that the general liability insurance policy the county had purchased would pay should the farm's buildings suffer damage during the event. The owner insisted the county obtain property insurance.

So Ms. Gray arranged for the county's property insurer, Affiliated FM, a unit of Johnston, R.I.-based FM Global, to add an endorsement to the county's property policy to cover the re-enactment at no additional cost.

FM did so, Ms. Gray said, because it understood that the general liability insurer would have been on the hook should the had the farm buildings suffered any damage.