פירוש על ברכות 59:10

"TALPIYYOT" IS THE HILL [TEL] TOWARD WHICH ALL MOUTHS [PIYYOT] TURN. The Gemara concludes that the verse “as the tower of David”, refers to the Bais Hamikdosh. לתלפיות literally means a landmark. The word can be divided in two תל פיות a hill (the temple mount) towards which all mouths turn, i.e. all our prayers are said in the direction of the temple. The Gemara in maseches Bovo Basro 25a has a discussion about where the Divine Presence is located. Some say in the west and some say in the east.
And we rule like this Gemara, and so too do we conclude in Lo Yachpor (Bovo Basro 25b), where the Gemara says you who live to the north of Eretz Yisroel should face south, towards Eretz Yisroel. And not like those amoroim mentioned earlier (Bovo Basro 25a) who argue whether the Divine Presence is in the east or in the west. According to those opinions we would always face west or east depending on which opinion we held. We however, face Yerusholayim always, no matter where we are and that follows our Gemara here and the conclusion of the Gemara on Bovo Basro 25b.
Tosfos was written in Europe. Now we are to the west of Eretz Yisroel, therefore we turn to the east when we pray.

The building towards which all mouths offer prayer. Some edd. read : a heap towards which all turn [ponim].