In ancient Roman religion, a lūcus (, plural lūcī) is a sacred grove. Lucus was one of four Latin words meaning in general "forest, woodland, grove" (along with nemus, silva, and saltus), but unlike the others it was primarily used as a religious designation. Servius defines the lucus as "a large number of trees with a religious significance," as distinguished from the silva, a natural forest, and a nemus, an arboretum that is not consecrated. A saltus usually implied a wilderness area with varied topographical features. A lucus was a cultivated place, more like a wooded park than a forest, and might contain an aedes, a building that housed the image of a god, or other landscaped features that facilitated or gave rise to ritual. It has been conjectured, for instance, that the Lupercal, referred to as a "cave," was a small lucus with an artificial grotto, since archaeology has uncovered no natural cave in the area. Apuleius records that "when pious travelers happen to pass by a sacred grove (lucus) or a cult place on their way, they are used to make a vow (votum), or a fruit offering, or to sit down for a while." What the Romans understood by religio lay in these ritual gestures, and not in contemplation. Etymology Some ancient sources as well as modern etymologists derive the word "from a letting in of light" (a lucendo); that is, the lucus was the clearing encompassed by trees. The Old High German cognate lôh also means "clearing, holy grove." Lucus appears to have been understood in this sense in early medieval literature; until the 10th century, it is regularly translated into OHG as harug, a word never used for the secular silva. Servius, however, somewhat perversely says that a lucus is so called because non luceat, "it is not illuminated," perhaps implying that a proper sacred grove hosted only legitimate daytime ceremonies and not dubious nocturnal rites that required torchlight. To clear a clearing In his book On Agriculture, Cato records a Roman ritual lucum conlucare, "to clear a clearing." The officiant is instructed to offer a pig as a piaculum, a propitiation or expiatory offering made in advance of the potential wrong committed against the grove through human agency. The following words are to be formulated (verba concipito) for the particular site: Whether thou be god or goddess (si deus, si dea) to whom this