Gradually these amplifications of culture spread: slowly to the north, more rapidly and completely to the south, into the similar environment of Colombia and Peru. Not all of the civilization devised in Yucatan and Guatemala, was carried into South America. Writing and time reckoning, for instance, never squeezed through the Isthmus, and the Incas got along with traditions and records of strings. On the other hand the South Americans, also growing populous and wealthy, added some culture elements of their own—bronze alloying, the hammock, the Pan’s pipe, the balance scale, the surgical art of trephining the skull, the idea of a vast, compactly organized empire.