四分律刪繁補闕行事鈔 1.257

1.257

一自然界者。未制作法已前，統通自然；或空有不同，水陸差別；後因難集，便開隨境攝，各有分限；人所至處，任運界起，故曰自然也。約處有四種不同，定量分六相差別，如〈集僧〉中。

First, the natural boundary (prakṛti-sīmā). Before rules for ritual demarcation were instituted, boundaries were naturally unified; or differentiated by whether an area was empty or inhabited, on water or on land. Later, because it became difficult to assemble, permission was given to delineate boundaries according to local terrain, each having its own limits. Wherever a person arrives, the boundary arises spontaneously; hence it is called 'natural'. Regarding locations, there are four different kinds; in terms of defining limits, they are divided into six different characteristics, as in the chapter 'Assembling the Saṃgha'.