Continuing, therefore, the same line of inquiry, and assuming that Mariette was right, and that the temple was really finally completed (and no doubt its axis revised) by the Ptolemies, and that they flourished about 200 B.C., we have the same problem. Was there a star towards which that temple could have been directed, and which could have been seen in that temple with its actual orientation? Calculation shows that the change of amplitude of Canopus due to the precessional movement between 1300 B.C. and 200 B.C. is almost exactly 1°, the difference in the amplitude of the temples. We seem, then, to have in the temples L and T two temples directed to the same star at different times. These statements must be taken as provisional only. To render them absolute, careful measurements must be made, on the spot, of the heights of the hills towards which the temples point. Leaving this for the moment on one side, we get in this manner astronomical dates of the reigns of Seti II. and Rameses III. within a very few years of those given by the Egyptologists. More than this, the application of this method entirely justifies Mariette's view with regard to these more modern temples at Thebes, and shows that when they were built the outlook was clear, so that the building ceremonials referred to in the last chapter might have been performed. I am next anxious to point out that not only is this so, but, accepting it, we can explain exactly why the walls and temples and columns were erected in the sequence which Mariette indicates. We not only know when they were built, but we can presently understand _why they were built_. The first point to which I draw attention in this matter is the following:--Referring to the plan, we find that before the time of Rameses III. the temple of Seti II. was right out in the open. It thus represented just one of those external rectangular temples which have been found at Denderah and at very many other places in Egypt. It was one of the Egyptian ideas to have two temples at right angles to each other. That temple, then, stood alone. The next change seems to have been this: The star Canopus, the setting of which it was built to watch, was, through the processional movement to which I have referred, no longer conveniently observed in that temple. To obviate this the temple T was built by Rameses III. with a change of amplitude equivalent to the actual precessional change of the star's declination, to carry on the observations.