Visitors to the Carnegie complex in Oakland can no longer use the main connection between its library and museum buildings, which the philanthropist purposefully linked 113 years ago.

Citing security concerns, Carnegie Museums officials on June 9 locked a doorway connecting the facilities, near the art museum's Hall of Architecture and the library's large print room. For years, visitors have been able to walk freely between the buildings, and many library users were dropped off at the museum's Carriage Drive entry, off Forbes Avenue.

Andrew Carnegie had the 1895 buildings interconnected -- with a library, music hall, art gallery and natural history museum -- as a "Noble Quartet," giving a well-rounded education to the working class.

Museums officials "acknowledge it's an inconvenience to some people," said Julie Hannon, Carnegie Museums corporate communications manager, but said the closing was necessary to aid security.

Ms. Hannon said the change was unrelated to the vandalism of a $1.2 million painting, apparently by a security guard, at Carnegie Museum of Art last month.