Davening At Gravesites

The Gemara[1] relates that Reish Lakish would mark the boundaries of where the Rabbis were buried. The simple meaning Rashi explains is that so Kohanim would not inadvertently walk over them thereby contracting Tumah.[2] R’ Yaakov Emden[3] (1697-1776) explains that Reish Lakish identified those graves so that people could daven by the graves of Tzadikim.

We find this idea in our Parsha by Kalev. To be saved from being persuaded by the עצת מרגלים; designs of the Megalim, Kalev davened over the קברי אבות; graves of the patriarchs.[4] Indeed, the Baal Haturim points out the end letters of חמת ויעלו בנגב ויבא;[5] they ascended in the south and he arrived at Chevron, spell אבות. 

Davening by their graves awakens the Tzadikim buried there so that they can be a good advocate for us. The place where Tzadikim are buried is holy and pure and the Tefila is accepted there more.[6] The חכמי התורה are themselves a dwelling for the Shechina even after their death as their burial place is fitting to find שפע; bounty, there. It is befitting for one to prostrate himself over the graves of Tzadikim and daven there because the Tefila is more acceptable there.[7] One should be careful, though, not to daven to the Tzadikim rather request from Hashem that he should have mercy in the merit of the Tzadikim buried there.[8]