Why the builders of Mycenae's Lion Gate left a giant triangle empty on purpose

In Greece, a stone gate built 3,300 years ago is still standing — and right above its entrance, the builders deliberately left a giant triangle empty. Why would anyone leave a hole in a fortress wall on purpose? Below the hole, a single 20-ton stone beam held up hundreds of tons of wall, and stone cracks when it bends. So they stopped strengthening the beam and stepped each layer inward from both sides, sending the weight around it and down into the ground. The famous lions? Just a very fancy plug. Sources: • Lion Gate — Wikipedia — https://en.wikipedia.org/wiki/Lion_Gate • e-mycenae.org Lions Gate — https://www.e-mycenae.org/lions-gate/ • Treasury of Atreus — Wikipedia — https://en.wikipedia.org/wiki/Treasury_of_Atreus • Corbel arch — Wikipedia — https://en.wikipedia.org/wiki/Corbel_arch