The main issue in MUSEUM is to present the very long History of Human Life in Mars. From its primitive evolution on the surface up to current (?) or very recent times in, of course, underground habitats. No History without dates; and to this end the LOH was set to distinguish between remote epochs when life was possible on the surface (from -2 Ga to -700 Ma) and the long millions of years when martians had to survive as troglodite inhabitants of deeper and deeper domes inside Mars. The line LOH provides the timing and basic dates; and central to such line is AP (=angel's plaza) which encodes the grandest numerical conundrums ever seen on Earth and learned from Cydonia (Mars). Art and mathematics (Number Theory and Geometry) are intertwined in the whole MUSEUM. In particular: the hand of Lecturer in this magnificent 'abstract bass-relief" is near the navel of the 'standing student' (marked with round, very large, button). That is a very subtle hint to the main core of geometrical diagrams intended between upper Monuments; namely, the 'golden section' G which is embedded in the human body (from navel to roots of hair at head). The reason for such fundamental hint is obvious: all diagrams and conundrums in MUSEUM are encoded in base-10 and the 'golden section' G is the mathematical side of inscribed 'regular decagon' in circle of radius unity. So that such idea of 'decimal system' has priority, as introduction, in the grand Lecture given at central Monument LECTIO.