What is "Sha'ar Sur"?
Rashi (from Yerushalmi Eruvin 5:1): This is the eastern gate of the Azarah, Sha'ar ha'Sarah 1 .
Targum Yonasan: It is the gate of Giborim. Radak - in Divrei ha'Yamim II, 23:5 it is called "Sha'ar ha'Yesod." Refer to 11:6:1:1*.
Radak (citing the Yerushalmi): it had seven names. It is called Sha'ar Sur, for Tamei people separated from there (they may not enter) - "Suru Tamei" (Eichah 4:15). It is called "Sha'ar ha'Yesod", for there they are Meyased (establish) the Halachah (the Sanhedrin sits there). It is called Sha'ar Charsis, for it is in line with the shining of the sun [in the morning] - "ha'Omer la'Cheres v'Lo Yizrach" (Iyov 9:7). It is called Sha'ar ha'Eisun, for it is used to enter and leave [the Azarah. Eisun is an expression of coming - "v'Asa me'Rivevos Kodesh" (Devarim 33:2). It is called Sha'ar ha'Tavech, for it is in the middle (between) two gates (of Ezras Nashim, and of the Heichal). It is called Sha'ar Chadash, for there Chachamim were Mechadesh a Halachah (that a Tevul Yom may not enter the Ezras Nashim). It is called Sha'ar Elyon, for it is l'Ma'alah (above) me'Ezras Yisrael. (Tosfos Yom Tov Midos 2:6 and others question this text, for it is not above Ezras Yisrael in Kedushah, nor in elevation. It seems that the Rambam's text (Hilchos Klei ha'Mikdash 7:6) was 'above Ezras Nashim.' - PF)
What is "Sha'ar Achar ha'Ratzim"?
Rashi: Also this is a gate of the Azarah. Yonason translates 'the gate that in back of if is Sha'ar ha'Ratzim.' Sha'ar ha'Ratzim is the path on which one goes from Beis ha'Melech to the Beis ha'Mikdash, like it says below (verse 19). In Divrei ha'Yamim II, 23:4, Sha'ar Achar ha'Ratzim is called Sha'ar ha'Sipim. Radak - it was in the south of the Azarah. It says about this in Divrei ha'Yamim I, 26:15 "Beis ha'Asufim." It was called Sha'ar ha'Ratzim at this time, for the Ratzim of the king were there.
To whom did he command to guard the Bayis?
Rashi: He commanded the first third.
What is the meaning of "Masach"?
Rashi: Guard very well, without Hesech Da'as (diverting the mind 1 ). The Mem is from the word (it is not a prefix). This is like "No'ash" (Shmuel II, 23:4) - without Yi'ush (despair).
Radak: This is guarding from Masach, i.e. destruction, like "v'Nisachtem me'Al ha'Adamah" (Devarim 26:63). Here it refers to demolition of the guarding "Pen Yehersu La'alos El Hashem" (Shemos 19:21). He warned them to guard like one, one by another. They should not separate from the order of guarding to go elsewhere.
Radak: From guarding the king.
