There are two uses of the SACRIFICE command, allowing you to make offerings to a deity on a larger scale, utilising a sacrificial fire. The first is done on your own, at a location marked by a god, the second - known as obeisance - a more profound spectacle performed while a deity presides over your efforts. The former is done alone, the latter generally undertaken in groups. The solitary sacrifice requires large batches of a valuable commodity (at least twenty) - the more sacrificed, the greater piety gain for the deity. The obeisance ritual, on the other hand, is performed either as part of a wider festival (see HELP FESTIVALS) or with the express purpose of aiding the presiding deity eroding the marks of a rival divinity.
The sacrificial fire should be made by the leading mortal in the group. This is done in the usual way for fire-building. The mortals present must then type OBEISANCE. All mortals in the location should be performing obeisance for the ritual to be truly effective. To enflame the fire sufficiently to honour the presiding deity, to bestow piety, and above all to weaken rival markings it it is necessary to sacrifice fine fabrics, hides, children or certain beasts: silk, wool or leather commodity for the fabrics (in batches of ten); babies, young boys and girls for the children; pigs, boars or goats for the beasts. Type SACRIFICE followed by the living animal, deceased child or fabric (in your inventory) to make your gesture; many iterations of the obeisance/sacrifice sequence are necessary to complete the ritual.
The piety gain from an obeisance ritual is felt immediately by the presiding deity. The erosion of another divinity's markings take a full Avalon year to spread through the location - you will be able to witness the progress when you type LOOK - and can be defeated by the opposing god arranging a counter-obeisance or by his/her priesthood organising a Festival of Consecration (often important if the defending god is likely to be absent a while).
If the obeisance is successful and unopposed for an Avalon year then the location's marks will be reduced - one point of reduction per Avalon year, per presided obeisance ritual - until none remain. At this point the location can be freely marked by any god providing a Festival of Holy Ground is undertaken by the priesthood and a full congregation. The Festival must be completed as a first act, then within an Avalon month the deity whose priesthood officiated the festival must place the mark; and finally a Festival of Consecration will render the divine marking permanent.
See HELP SHRINES for info on the various holy constructions (from shrines to temples to cathedrals to monasteries) and HELP OFFERING, HELP TEMPLES, and HELP DEVOTIONS for instructions on pious activity and HELP FESTIVALS for details of the many holy festivals available to priesthood and requiring congregation to carry through.