B'nei Yisrael are commanded (27:4) that after they cross the Yardein they are to set down the rocks on Har Eival, etc. In the gemara Sanhedrin 44a, R' Shaila teaches that Yehoshua did not act accordingly as the pasuk instructed to perform this ceremony immediately after crossing the Yardein but he travelled for 60 mil. Tosafos asks an obvious question. B'nei Yisrael were clearly commanded to follow these proceedings on Har Grizim and Har Eival. Is it Yehoshua's fault that these mountains were 60 mil from the Yardein?

Tosafos puts together a rather creative answer. In the gemara (Sotah 33b) there is a dispute between R' Yehuda and R' Elazar. R' Yehuda holds that Har Grizim and Eival were far away from the Yardein while R' Elazar holds that they were right next to it. Tosafos explains that R' Elazar holds that there were two sets of mountains and that they carried out the commandment on the closer one. The Yerushalmi states that according to R' Elazar, they actually built two mountains upon crossing the Yardein and called one Grizim and one Eival. Tosafos explains that R' Shaila here is of the opinion that the commandment to B'nei Yisrael follows R' Elazar's interpretation and was supposed to be carried out on the nearer mountain. What they in fact did in practice follows R' Yehuda's interpretation and that is why Yehoshua is rebuked for having delayed 60 mil. He was expected to have performed the ritual on the nearer set of mountains.