Written language
Egyptians were the artistic painters. They drew the objects and animals unusually true. The first inhabitants of the Nile valley fixed their thoughts depicting the objects on the picture about which they talked.
But by the period of the Early Kingdom the Egyptian system of writing formed. It was rather complicated at first sight. It contained a lot of different signs from the depiction of people and animals to objects of the every-day life. Sometimes it seems that there is no way to understand such combination of signs. It took more than 2 thousand years to find out the mysteries of Egyptian writing.
Results, Egyptians were the first whose signs fixed sounds. But it didn't turn into the fully sound writing. The main reason was that Egyptians as well as many other nations didn't write vowel sounds. That is why people wrote the sign that explained the written signs.
There were also signs that fixed several sounds simultaneously. The consonants were the base of the word and Ancient Egyptians could understand perfectly the word just looking at it. Egyptians were the first to make the alphabet that had 25 letters.
Egyptians were the first in the world that managed to express the abstract notion through the concrete sign. For example, there was the sign (the roll of papyrus with stamp) that meant any abstract notion. Such complicated system of writing as the reason why it took so much time to decode hieroglyphs.