Genoese Crossbowmen
An illustrious military unit of the Genoese Republic was called the Balestrieri Genovesi (Italian). For both foreign and other Italian powers, they served as mercenaries. The Genoese were well-known for being highly accomplished professionals as well as being generally accessible and plentiful. The maritime prowess of Genoa appears to have contributed to the high numbers of professional crossbowmen.
Genoese legislation stipulated a minimum number of crossbowmen that galleys had to carry. There is no question that the employment of the crossbow was associated with the city's naval and commercial success, although the existence of such a ban does not imply that it was always adhered too strictly.
They had substantial pavise shields (scudo pavese, in Italian). Crossbows require less raw strength to operate than longbows, making them simpler to employ. But even so, loading a medieval crossbow should hardly be seen as simple.