Kerma maintained it's independence from Egypt for approximately 400 years, until the beginning of the Third Intermediate Period. With the decline of Egypt's power in the south the Kingdom of Kush filled in the void and annexed Kerma in the process.
Nubian grave goods during this period included cattle skulls, which is where the image on the banner originated from. The significance of the four gold diamonds along the top is unknown. They could have represented the four corners of the city, had some sort of religious or cultural significance, or just been chosen for aesthetic reasons.
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Sean Sherman has been a fan of alternate timelines ever since seeing Spock with a goatee. By day he is a CPA, at night he explores the multiverse and shares his findings over at his blog, Other Times.