Deuteronomy 27:2

Thou shalt set thee up great stones - How many is not specified, possibly twelve, and possibly only a sufficient number to make a surface large enough to write the blessings and the curses on.

Plaster them with plaster - Perhaps the original ושדת אתם בשיד vesadta otham bassid should be translated, Thou shalt cement them with cement, because this was intended to be a durable monument. In similar cases it was customary to set up a single stone, or a heap, rudely put together, where no cement or mortar appears to have been used; and because this was common, it was necessary to give particular directions when the usual method was not to be followed. Some suppose that the writing was to be in relievo, and that the spaces between the letters were filled up by the mortar or cement. This is quite a possible case, as the Eastern inscriptions are frequently done in this way. There is now before me a large slab of basaltes, two feet long by sixteen inches wide, on which there is an inscription in Persian, Arabic, and Tamul; in the two former the letters are all raised, the surface of the stone being dug out, but the Tamul is indented. A kind of reddish paint had been smeared over the letters to make them more apparent. Two Arabic marbles in the University of Oxford have the inscriptions in relievo, like those on the slab of basalt in my possession. In the opinion of some even this case may cast light upon the subject in question

The stones here named are not those of which the altar Deuteronomy 27:5 was to be built, but are to serve as a separate monument witnessing to the fact that the people took possession of the land by virtue of the Law inscribed on them and with an acknowledgment of its obligations.

27:2 On that day - About that time, for it was not done 'till some days after their passing over.