or during epidemics, or on battlefields. Otherwise the ustrinum was supposed to be cleared after use, to avoid the mixing of ashes from different bodies, though a few cases are known in which this was deliberately done. Caracalla deliberately mixed the ashes of his brother Geta with those of his executed supporters, as a final insult. On the other hand, a few examples are known of couples whose ashes were contained in the same vessel, as an expression of love. Inhumation was practiced regularly in archaic Rome, but in the Mid- to Late Republic and the Empire into the 1st and 2nd centuries, cremation became the most common burial practice. Toynbee describes the change from burial to cremation as generally starting, excepting a few noble families, by 400 BC. Patrician members of the gens Cornelia continued inhumating their dead until 79 BC, when the dictator Sulla became the first patrician Cornelius to be cremated, perhaps because he feared that otherwise his body would be defaced by supporters of his arch-enemy, Gaius Marius. The ancient Sepulcretum, in the Roman Forum, shows evidence of both inhumation and cremation, and laws relating to both practices go back to the 5th century BC. Cremation was far more costly and time-consuming than inhumation; at its simplest and least costly, inhumation required little more than a scraped hollow in the ground, with some form of covering. The planning and execution of cremations required expertise. The unplanned cremations of Pompey and Caligula left their bodies part-burnt for want of sufficient fuel or skill. Wood for pyres was expensive; on average, an effective, well built pyre employed about half a cord of timber - and once lit, it must be tended for 8 or 9 hours to ensure that the body was completely consumed. For cremations of the elite, coin and sculptural evidence for pyres usually shows eight layers of timber, each laid at right angles to those above and below, with the whole resembling an altar and the body at least partly concealed within. The smoke of the pyre could be sweetened with aromatic herbs, leaves and libations. For the elite, incense could be burnt; it not only masked unpleasant smells, but being resinous was highly flammable. At Ostia, and probably elsewhere, municipally funded funerals for ex-officials were sometimes granted up to 50 pounds of incense. For the highest status cremations, pyres of several storeys were built,