Aon Corp.’s risk-management unit is acquiring Allied North America, the Jericho, N.Y.-based broker that specializes in construction. After the deal is closed, Aon will place Allied’s chairman, Bill Marino, in the dual role of president of Aon’s global construction business and vice chairman of Aon Construction Services Group.

“Through the increased brokering capability provided by Allied North America, we are enhancing our global construction powerhouse as well as our abilities to better serve our clients and grow our business around the world,” says Gregory C. Case, Aon Corp.’s CEO. Steve McGill, CEO of Aon Risk Services, says the deal “reinforces” Aon’s already-strong position in construction. The acquisition is scheduled to close before the end of 2009. The price was not disclosed.

Aon is the biggest insurance broker, according to A.M. Best, Oldwick, N.J., a global credit-rating organization dedicated to the financial-services industry. Aon now will add another $850 million in property/casualty premiums that come with Allied, according to Insurance Journal, an industry publication. Founded in 1979, Allied from the start concentrated on construction insurance and contract surety.

In 1998, Peter Arkley, chairman and CEO of Aon Construction Services Group, created the Aon Construction Program Group, taking Aon into insurance underwriting in general liability, workers’ compensation and auto-liability coverages. But the company sold the group in late 2006 to Old Republic Insurance Co.

Since then Aon has focused on brokerage, working on multiple continents. It now also has offices in Holland, Australia and Canada.

Marino says Allied needed a global platform. “More and more of our clients are global in nature and our 16 offices were limited to the U.S.,” he says. “The largest contractors are global.”

“It was a strategic acquisition for us,” says Arkley. “We saw Allied as a strong competitor and respected its technical ability and perspective.”