A structure comprising a stack of composite plies of fiber-reinforced matrix material. The structure includes reinforcing inserts and holes. Each reinforcing insert is embedded in the stack and bonded to the stack, and each hole passes through a respective one of the reinforcing inserts. A support layer is joined to each reinforcing insert. The support layer is formed from a different material to the composite plies and impregnated with the same matrix material as the composite plies. The support layer carries the inserts during the assembly of the structure, and can assist in a process of infusing and/or curing the stack.