You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Iran

Context:
The emergence of Susa as a city, as determined by radiocarbon dating, dates back to early 4,395 BC. There are dozens of prehistoric sites across the Iranian plateau, pointing to the existence of ancient cultures and urban settlements in the 4th millennium BC. During the Bronze Age, Iran was home to several civilizations including Elam, Jiroft, and Zayande River. Elam, the most prominent of these civilizations, developed in the southwest of Iran, alongside those in Mesopotamia. The emergence of writing in Elam was paralleled to Sumer, and the Elamite cuneiform was developed since the 3rd millennium BC.

Question:
How long ago did ancient cultures and settlements exist across the Iranian plateau?

the 4th millennium BC