Simplify the following text for a Grade 10 native English-speaking person.
Original: The period comprises two phases , the 11th Dynasty , which ruled from Thebes and the 12th Dynasty onwards which was centered around el-Lisht .
Simplified: The period had two phases , the 11th Dynasty , which ruled from Thebes and the 12th and the following dynasties which were centred around el-Lisht .