Humans have been coming up with novel ideas for uses of technology since the beginning of time. They can all be considered to be inventions, but inventions as we know them today started in the 15th century.
Some will argue that the first recorded inventions were in Italy, but the first recorded patent record was actually a patent letter granted to John of Utynam in 1449. King Henry VI of England granted the patent for a 20 year monopoly detailing the manufacture of stained glass that was used for the windows at Eton College. The document was sealed with the King's Great Seal.
This patent was the beginning of the current patent system where a government grants a limited monopoly in exchange for publishing the technology for access by anyone. This leads to more discovery and more inventions.