These are called “keystone” cuts, and are Metal expansion locks. They have been observed in ancient Egypt, and ancient Peru/Bolivia (with bronze, not lead).
Because of these things existing on opposite ends of the world, many believe ancient Peru/Bolivia had contact with ancient Egypt or other ancient cultures.
They make cavities then a piece of iron is forged with the shape of the cavities but smaller in size, the piece of iron is placed in the cavities and then is poured the lead. I live in Rome and the Colosseum and all the other building made by the Romans are all made, where is required, using this ancient tech. we were far more advanced millennia ago but knowledge was destroyed or lost to the sands of time. look up the great library in alexandria… it burned and was said to hold the knowledge from places like this.
Broad dove-tail clamp with iron bar and lead, (Persepolis, Platform)
1: vlad9vt: atlantis.https://www.youtube.com/watchapp=desktop&v=dtgDe2S0KQY&fbclid