Wikipedia
Aes rude ( Latin, "rough bronze") was a nugget of bronze used as a sort of proto- currency in ancient Italy during the gradual transition from bartering to the use of round coinage made from precious metals.
The Italian economy of the time (late middle first millennium BC) was based on a bronze standard (unlike the silver standards in use in contemporary Greece, the Aeginetan standard and its competitor the Attic standard). Consequently, unworked lumps of bronze were used as both primitive ingots and as primitive coins, facilitating trade across the peninsula and paving the way for the first true Roman ingots, the aes signatum, which, in turn, was the precursor of the first Roman true coinage, the aes grave.
The earliest surviving piece of aes rude dates from the early 8th century BC and as late as the late 4th century BC, and was cast in central Italy. It is, simply, bronze, shaped vaguely like a lumpy ingot. Only later on did it become usual to mark these lumps and, eventually, make them into a standard shape (the round, thin disk-shape still in use today).