Possible Clues:

• Central block at the summit of an arch
• Summit block in an arch
• Important piece in an arch
• Island's character is essential element
• After opener stumped, single that is vital to stability
• Central building block at the top of an arch
• Florida island's mood -- everything depends on it
• Film Kop supporter?
• Pennsylvania is known as the ____ state
• '-- Cops', a silent film series