The following passage in a book was brought to my attention:
Quote:Trainiert wurde nach den Lehrbüchern der Antike, insbesondere dem Buch "Über das Militärwesen" (de re militari) des Vegetius aus dem vierten Jahrhundert, das hundertfach abgeschrieben und verbreitet wurde. Es beschreibt auch die Belagerungstechniken und die dafür erforderlichen Geräte. Daran konnte sich Karl der Grosse orientieren, wenn der den Einsatz von Steinschleudern (fundibulae) und die Bereitstellung von geeigneten Steinen anforderte. (Superscript 14)
--- Rough english translation:
Training was performed after the teaching books of the antiquity, e.g. the book de re militari of Vegetius of the 4th century ... .It describes also siege techniques and the therefore used tools. Charlemagne could have oriented himself at this text, when he commanded the fielding of slings (fundibulae) and the provisioning of suitable stones. (superscript 14)
Note 14: MGH Capitularia 1, Nr. 77
(MGH stands for monumenta germaniae historica)
Source: Karl der Grosse: Der heilige Barbar, Stefan Weinfurter, Piper 2013, ISBN-13: 978-3492055826, p. 82
Link to the original Latin source:
https://www.dmgh.de/de/fs1/object/display/bsb00000820_00183.html?sortIndex=020%3...line 29 ff
... fundibulas, et illos homines qui exinde bene sciant iactare. Et marscalci regis adducant eis petras in saumas viginti, si opus est.
My latin is a bit rusty, so don't quote me on the following translation.
The latin source states what shall be brought as supplies in carriages. ... Slings, and those men who know well how to throw. The marshals (horseleaders?) of the reign shall bring twenty mule loads of stones, if necessary.
If someone is interested in this time period he might follow up on that.