If we're talking about the earliest system of symbols with a direct, one-to-one correspondence with spoken language, then the answer is likely cuneiform**.
Cuneiform, developed by the ancient Sumerians around 3500 BCE, is known for its distinctive wedge-shaped marks made with a stylus on clay tablets. It evolved from a system of pictographs and eventually became a sophisticated writing system capable of representing not only words but also sounds.
However, if we consider pre-writing systems like proto-writing to be "written language", then the earliest forms are even older. These systems used symbols to convey information but didn't necessarily have a direct, one-to-one correspondence with spoken language.
Some examples of pre-writing systems include:
* The Vinča symbols, dating back to 5500 BCE, found in the Balkans, which may have been used for accounting or other record-keeping.
* The Indus script, dating back to 3500 BCE, found in the Indus Valley Civilization, which remains undeciphered.
* The proto-Sinaitic script, dating back to 1800 BCE, which is considered the precursor to the Phoenician alphabet.
Ultimately, the definition of "written language" is somewhat subjective. While cuneiform is often considered the first true written language, it's important to remember that earlier systems of symbols played a crucial role in the development of writing.