A security barrier (1, 47) comprising: a substantially planar support element having a top edge and a bottom edge; and a bulbous barrier element, the barrier element having a top edge and a bottom edge, with a curved protruding section extending between the top and bottom edges, the protruding section extending away from the plane containing the top and bottom edges, wherein: the support element and barrier element are integrally or unreleasably connected to each other at a connection region at or near their top edges and define an internal space therebetween which may receive a generally planar structure having a top edge, and wherein the security barrier may be rested on the structure so that the connection region lies on or near the top edge of the structure, with the support element and the barrier element lying on opposing sides of the structure, with the support element lying close to the plane of the structure and the protruding section protruding outwardly from the plane of the structure; characterised in that a bracing element (41, 48) extends between the inner surface of the barrier element and the inner surface of the support element, spaced above the bottom edges thereof, into the internal space between the support element and the barrier element, and assists in bracing the security barrier. a substantially planar support element having a top edge and a bottom edge; and a bulbous barrier element, the barrier element having a top edge and a bottom edge, with a curved protruding section extending between the top and bottom edges, the protruding section extending away from the plane containing the top and bottom edges, wherein: the support element and barrier element are integrally or unreleasably connected to each other at a connection region at or near their top edges and define an internal space therebetween which may receive a generally planar structure having a top edge, and wherein the security barrier may be rested on the structure so that the connection region lies on or near the top edge of the structure, with the support element and the barrier element lying on opposing sides of the structure, with the support element lying close to the plane of the structure and the protruding section protruding outwardly from the plane of the structure; characterised in that a bracing element (41, 48) extends between the inner surface of the barrier element and the inner surface of the support element, spaced above the bottom edges thereof, into the internal space between the support element and the barrier element, and assists in bracing the security barrier. the support element and barrier element are integrally or unreleasably connected to each other at a connection region at or near their top edges and define an internal space therebetween which may receive a generally planar structure having a top edge, and wherein the security barrier may be rested on the structure so that the connection region lies on or near the top edge of the structure, with the support element and the barrier element lying on opposing sides of the structure, with the support element lying close to the plane of the structure and the protruding section protruding outwardly from the plane of the structure; characterised in that a bracing element (41, 48) extends between the inner surface of the barrier element and the inner surface of the support element, spaced above the bottom edges thereof, into the internal space between the support element and the barrier element, and assists in bracing the security barrier.