Archicortex is a type of cortical tissue that consists of three cortical laminae (layers of neuronal cell bodies). It has fewer laminae than both neocortex, which has six, and paleocortex, which has either four or five. Archicortex, along with paleocortex and periallocortex, is a type of allocortex. Because the number of laminae that compose a type of cortical tissue seems to be directly proportional to both the information-processing capabilities of that tissue and its phylogenetic age, archicortex is thought to be the oldest and most basic type of cortical tissue.
Archicortex is most prevalent in the olfactory cortex and the hippocampus, which are responsible for processing smells and forming memories, respectively. Because olfaction is considered to be the phylogenetically oldest sensory modality, and the limbic system, of which the hippocampus is a part, is one of the oldest systems in the brain, it is likely that archicortex was one of the first types of tissue to develop in primitive nervous systems.