“You are right, Porthos; and you are quite a padlock for safety.  But, to revert to yourself?”

“Yes,” said Porthos.

“You said just now you came hither to study topography?”

“I did so.”

“Tudieu! my friend, what fine things you will do!”

“How do you mean?”

“Why, these fortifications are admirable.”

“Is that your opinion?”

“Decidedly it is.  In truth, to anything but a regular siege, Belle-Isle is absolutely impregnable.”

Porthos rubbed his hands.  “That is my opinion,” said he.

“But who the devil has fortified this paltry little place in this manner?”

Porthos drew himself up proudly:  “Did I not tell you who?”

“No.”

“Do you not suspect?”

“No; all I can say is that he is a man who has studied all the systems, and who appears to me to have stopped at the best.”

“Hush!” said Porthos; “consider my modesty, my dear D’Artagnan.”

“In truth,” replied the musketeer, “can it be you — who — oh!”

“Pray — my dear friend — "

“You who have imagined, traced, and combined between these bastions, these redans, these curtains, these half-moons; and are preparing that covered way?”

“I beg you — "

“You who have built that lunette with its retiring angles and its salient edges?”

“My friend — "

“You who have given that inclination to the openings of your embrasures, by means of which you so effectively protect the men who serve the guns?”

“Eh! mon Dieu! yes.”

“Oh!  Porthos, Porthos!  I must bow down before you — I must admire you!  But you have always concealed from us this superb, this incomparable genius.  I hope, my dear friend, you will show me all this in detail.”

“Nothing more easy.  Here lies my original sketch, my plan.”

“Show it me.”  Porthos led D’Artagnan towards the stone that served him for a table, and upon which the plan was spread.  At the foot of the plan was written, in the formidable writing of Porthos, writing of which we have already had occasion to speak:  —

“Instead of making use of the square or rectangle, as has been done to this time, you will suppose your place inclosed in a regular hexagon, this polygon having the advantage of offering more angles than the quadrilateral one.  Every side of your hexagon, of which you will determine the length in proportion to the dimensions taken upon the place, will be divided into two parts, and upon the middle point you will elevate a perpendicular towards the center of the polygon, which will equal in length the sixth part of the side.  By the extremities of each side of the polygon, you will trace two diagonals, which will cut the perpendicular.  These will form the precise lines of your defense.”

“The devil!” said D’Artagnan, stopping at this point of the demonstration; “why, this is a complete system, Porthos.”