in supporting their views. Adding more difficulty to their interpretation is the obscure language they used. Plato paraphrased the pre-Socratics and showed no interest in accurately representing their views. Aristotle was more accurate, but saw them under the scope of his philosophy. Theophrastus, Aristotle's successor, wrote an encyclopedic book Opinion of the Physicists that was the standard work about the pre-Socratics in ancient times. It is now lost, but Simplicius relied on it heavily in his accounts. In 1903, the German professors H. Diels and W. Kranz published Die Fragmente der Vorsokratiker (The Fragments of the pre-Socratics), which collected all of the known fragments. Scholars now use this book to reference the fragments using a coding scheme called Diels–Kranz numbering. The first two characters of the scheme are "DK" for Diels and Kranz. Next is a number representing a specific philosopher. After that is a code regarding whether the fragment is a testimonia, coded as "A", or "B" if is a direct quote from the philosopher. Last is a number assigned to the fragment, which may include a decimal to reflect specific lines of a fragment. For example, "DK59B12.3" identifies line 3 of Anaxagoras fragment 12. A similar way of referring to quotes is the system prefixed with "LM" by André Laks and Glenn W. Most who edited Early Greek Philosophy in 2016. Collectively, these fragments are called doxography (derived from the latin doxographus; derived from the Greek word for "opinion" doxa). Historical background Philosophy emerged in ancient Greece in the 6th century BCE. The pre-Socratic era lasted about two centuries, during which the expanding Persian Achaemenid Empire was stretching to the west, while the Greeks were advancing in trade and sea routes, reaching Cyprus and Syria. The first pre-Socratics lived in Ionia, on the western coast of Anatolia. Persians conquered the towns of Ionia c. 540 BCE and Persian tyrants then ruled them. The Greeks revolted in 499 BCE, but ultimately were defeated in 494 BCE. Slowly but steadily Athens became the philosophical center of Greece by the middle of the fifth century. Athens was entering its Classical Era, with philosophers such as Socrates, Plato, and Aristotle, but the impact of the pre-Socratics continued. Several factors contributed to the birth of pre-Socratic philosophy in Ancient Greece. Ionian towns, especially Miletus, had close trade relations with Egypt and Mesopotamia, cultures with observations about the natural world that differed from those