Egyptians believed that they had eternal spirits which made them think that they could rule the world even after they were dead and that whatever they had in this life they would need in the next. Therefore, they stuffed there tombs full of stuff to use in the afterlife
I hope you are not referring to the Great Pyramids because contrary to popular believe there are no Tombs inside the Pyramids. The Egyptians did create vast underground tombs that were fill with everything someone might need in the afterlife. Prized pets and servants were killed and placed in the tomb so they could serve their masters.
