The Amenemhet III pyramid at Hawara. It had an inner core of mudbricks and an outer veneer of limestone. Over the centuries, the outer veneer has fallen away exposing the inner core of mudbricks. Millions of mudbricks went into making this pyramid. The Israelites were slaves in Egypt at this time and it is likely that the Israelites made the mudbricks used to build this pyramid. After the exodus of the Jews in the 13th dynasty, there was not enough slave labor to build pyramids and so the Pyramid Age ended. Interestingly, the very first pyramid built in Egypt was probably designed by an Israelite too: Joseph (Imhotep) designed the Step Pyramid in the 3rd dynasty. The pyramids of the Old Kingdom were made from solid limestone using Egptian labor and they have stood the test of time a lot better than the pyramids of the Middle Kingdom (12th dynasty) which were made from mudbricks with only a limestone veneer. The pyramid age coincides with Israel's sojourn in Egypt.