A masonry wall system includes a plurality of blocks. Each block has two external side walls and is adapted for use adjacent to further said blocks such that the side walls form at least one wall surface of a wall structure (40) constructed from the blocks. A plurality of the blocks include a tongue (8) projecting from a sidewall thereof. The blocks can be arranged such that a plurality of the tongues (8) combine to form a plurality of furring ridges (42) on the wall structure having a required spacing therebetween. In a preferred embodiment the spacing between the furring ridges (42) is greater than the length of the longest of the blocks used. A method of assembling a masonry wall is also disclosed.