The health of the city was promoted by spacious openings and squares, in which a numerous population from the capital and the distant country assembled to celebrate the high festivals of their religion. For Cuzco was the "Holy City"; 19 and the great temple of the Sun, to which pilgrims resorted from the furthest borders of the empire, was the most magnificent structure in the New World, and unsurpassed, probably, in the costliness of its decorations by any building in the Old. Towards the north, on the sierra or rugged eminence already noticed, rose a strong fortress, the remains of which at the present day, by their vast size, excite the admiration of the traveller.20 It was defended by a single wall of great thickness, and twelve hundred feet long on the side facing the city, where the precipitous character of the ground was of itself almost sufficient for its defence. On the other quarter, where the approaches were less difficult, it was protected by two other semicircular walls of the same length as the preceding. They were separated, a considerable distance from one another and from the fortress; and the intervening ground was raised so that the walls afforded a breastwork for the troops stationed there in times of assault. The fortress consisted of three towers, detached from one another. One was appropriated to the Inca, and was garnished with the sumptuous decorations befitting a royal residence, rather than a military post. The other two were held by the garrison, drawn from the Peruvian nobles, and commanded by an officer of the blood royal; for the position was of too great importance to be intrusted to inferior hands. The hill was excavated below the towers, and several subterraneous galleries communicated with the city and the palaces of the Inca.21 The fortress, the walls, and the galleries were all built of stone, the heavy blocks of which were not laid in regular courses, but so disposed that the small ones might fill up the interstices between the great. They formed a sort of rustic work, being rough-hewn except towards the edges, which were finely wrought; and, though no cement was used, the several blocks were adjusted with so much exactness and united so closely, that it was impossible to introduce even the blade of a knife between them.22 Many of these stones were of vast size; some of them being full thirty-eight feet long, by eighteen broad, and six feet thick.23