Someone who stands in the courtyard of a catacomb is tahor as long as it is four cu-bits, according to Beis Shammai’s opinion. Beis Hillel say: Four handbreadths. [If] a beam was used as a cover for a grave, whether it is standing upright or lying on its side, nothing becomes tamei except what is opposite the opening [of the grave]. [If] one end [of the beam] was made into a golel for a grave, only four hand-breadths of the beam become tamei, provided that the rest is going to be chopped off. R’ Yehudah says: It is all regarded as one unit.