In anatomy of animals, the archipallium or archicortex is the phylogenetically the oldest region of the brain's pallium or cortex.

The archipallium or archicortex is often considered contiguous with the olfactory cortex, but the extent of the archipallium varies among species. In older species, such as fish, the archipallium makes up most of the cerebrum. Amphibians develop an archipallium and paleopallium, whereas reptiles develop an archipallium, paleopallium and a primitive neopallium.

In humans, the archipallium makes up the hippocampus.

Archicortex is also defined as 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.