Kukai’s plan was that his monastic center on Mount Koya would be a large-scale physical representation of the two mandalas that were important in Shingon ritual.
The two mandalas in Shingon ritual were known as the Kongokai (Diamond mandala) and Taizokai (Womb mandala).
The Kongokai mandala depicted the universe of the five Wisdom Buddhas (the rulers of the heavenly realms in the universe), while the Taizokai was for the five Wisdom Kings that protected each of them