The upper chambers of Great Pyramid remained sealed until Al-Mamoun and his men tunneled around the granite blocks in 820 AD, opening the upper chambers for all time. But was it the first time that the upper chambers had been explored? Consider the fact that the well shaft is smooth, well carved, and has a purposeful direction until it reaches the grotto, about half way up. Then the tunneling becomes roughly hewn and directionless until it reaches the Grand Gallery. I believe that someone or a group with a little trigonometry in their heads figured out how to get to the upper chambers and eventually did. Z. Sitchin writes that Lord Marduk was imprisioned in the pyramid and that his followers freed him by tunneling up the well shaft. If that was the case, then why isn't the upper half of the well shaft as smooth and direction oriented as the lower half. The original tunnelers almost missed the Grand Gallery. It could have been the Greeks or the Romans or a group of treasure hunters. Finding nothing, they abandoned the project. But the well shaft remained opened (possibly filled with a lot of debris) for Al-Mamoun and for all who walked down the descending pathway. How Al-Mamoun and his men missed this, is for speculation.Your coments, as always, are welcomed. It has recently occured to me that the roughly hewn part may have been originally a small connecting passageway between the "grotto" and the Grand Gallery, enough to get a connecting wire through. This raises the possiblity that the pit (a repository?) had additional purpose. Why a connection betwen the "grotto" and the Grand Gallery? Good question.