Abstract: A building block (2) comprising two side panels (6, 8) with at least one open side, the side panels spaced apart by two bridging parts (10, 12), a removable section (17) on at least one bridging part (10, 12), and a pair of recessed or protruding formations (20) on opposite inner faces of the open end of the side panels (6, 8) to enable building blocks to be interconnected. A location device (40) comprising two members (44) spaced apart by cross members (42), where the two members (44) extend beyond the cross members (42) to engage with formations (26) of one or more building blocks (2) is also disclosed. A wall constructed from building blocks (2) and utilising location devices (40) and a method of constructing such a wall are similarly disclosed.