What thoughts must crowd on the mind of the traveller as he wanders amidst these memorials of the past; as he treads over the ashes of the generations who reared these colossal fabrics, which take us from the present into the very depths of time! But who were their builders? Was it the shadowy Olmecs, whose history, like that of the ancient Titans, is lost in the mists of fable? or, as commonly reported, the peaceful and industrious Toltecs, of whom all that we can glean rests on traditions hardly more secure? What has become of the races who built them? Did they remain on the soil, and mingle and become incorporated with the fierce Aztecs who succeeded them? Or did they pass on to the South, and find a wider field for the expansion of their civilization, as shown by the higher character of the architectural remains in the distant regions of Central America and Yucatan? It is all a mystery,--over which time has thrown an impenetrable veil, that no mortal hand may raise. A nation has passed away,--powerful, populous, and well advanced in refinement, as attested by their monuments,--but it has perished without a name. It has died and made no sign! Such speculations, however, do not seem to have disturbed the minds of the Conquerors, who have not left a single line respecting these time-honored structures, though they passed in full view of them,--perhaps under their very shadows. In the sufferings of the present they had little leisure to bestow on the past. Indeed, the new and perilous position in which at this very spot they found themselves must naturally have excluded every other thought from their bosoms but that of self-preservation.