Help needed building an onager

[PhilusEstilius]

That onager ball is no longer where the picture shows it for a friend and I threw it over the gate and hid it amongst undergrowth, and it is well we did for the farmer or land owner later removed all the Roman stonework from what had been a bridge over a stream 20 meters away and may well have thrown that also.

I have to say that it did take both of us to lift it at 35cm diameter which does make one understand just how heavy a job it would have been loading these onager weapons so the rate of fire was not so rapid.