In the fifth aliyah Moshe gives a lot of "behind the scenes" detail of what went on during the giving of the Ten Commandments at Mt. Sinai. It says here that G-d spoke the words out of the midst of fire and thick darkness and with a great voice. The words were written on the two luchos (tablets). During this, the heads of the tribes came to Moshe and told him that they don't think they can survive such a great revelation. They said that Moshe, alone, should hear the rest of the Torah directly from G-d, and afterward, to tell it to them and they will do it.