There is a square tower in one of the inner courts which must be considered as the most singular structure in Palenque. In position and manner of construction it is abnormal in character. It was probably intended for some special object, after the monastery had been completed. When Captain Del Rio saw this tower, in 1787, he estimated its height to be sixteen yards. In 1870 there were heaps of rubble and fallen stones piled against the base, which made it difficult for me to make exact measurements, but an approximate estimate gave the sides of the square near the base as twenty-three feet, and the height about forty-five feet. The peculiarity about the construction is the fact that it consists of a tower within a tower. The inner structure contains a steep and narrow staircase. Light is obtained through large openings in the sides of the outer tower, and then through smaller openings in the walls of the interior one. The steps appear to have led up to the top. The walls are formed of rough slabs of limestone which had been thickly coated over with cement, portions of which still remained. It was raised to a height which commanded views of the adjacent temples. Upon my return to the eastern front, I found that the Indians had slung the hammocks in the outer corridor overlooking the forest. A few minutes before sunset we heard the strange and beautiful notes of a solitary bird singing amongst the ruins. The song resembled in its tone that of a thrush. Dr. Coller said that the bird was a kind of nightingale, and that it was only known to live within and around the Palenque temples. The bird sang in a slow, deliberate manner, each of the notes having a short interval of time between them. The song was maintained during the twilight, and ceased as soon as it became dark and the night had begun. It was an evening hymn to the setting sun. The hoarse screams and movements of troops of monkeys then disturbed the precincts. These harsh noises gradually stopped, and as the night advanced the forest became silent. The moon was up and we knew that it was shining brightly above the trees, but we could only see occasionally its faint glimmer. I had expected to hear the croaking of frogs or the sounds of cicadas, the usual accompaniment to a tropical evening, but although there was a running stream of water at the foot of the mound, these familiar sounds were absent.