Nonetheless, even when they did not sponsor academies, Renaissance lords and patrons often had a particular interest in scientific works and treatises, especially those devoted to subjects of military value (such as the works on metalworking by Vannoccio Biringuccio and George Agricola, or Niccolò Tartaglia’s treatise on ballistics, in the mid-sixteenth century), or booklets dedicated to parva naturalia which were intended as forms of intellectual entertainment and usually contained descriptions of miranda naturae or astrological predictions. Exceptional natural events such as earthquakes—a famous one occurred in Pozzuoli in 1537—led to the publication of a number of short treatises which interpreted the calamity as either a natural phenomenon or as a sign sent by the celestial influences: these works were particularly sought after by powerful men who wanted to be reassured about the significance of natural events and their possible consequences. Several Renaissance rulers cultivated an interest in sciences like alchemy, and patronized or participated first-hand in investigations of the natural world: disciplines like zoology, which depended on the collection of material, information, and drawings, relied particularly heavily on the sponsorship of the wealthy and powerful. The zoological and botanical works and catalogues which, though composed by university professors, started from the 1540s to circulate around Europe, were often addressed to or sponsored by rulers who had the means to employ artists and other specialists needed to complete these costly volumes. Drawings were not simply ornaments to a text, but a necessity for accurate classification of plants and animals.