Gemara

Rav Ada of Yafo: The 10 sons of Haman and the word "v'Aseres" must be read in one breath, because they died at the same moment.

R. Yochanan: The 'Vov' of "Vayzasa" must be stretched (like a long rod - the text of the Rif and Rosh omits this), because they were all hung on one gallows.

R. Chanina bar Papa: All Shirim are written half-brick (the writing) on top of brick (the blank part), and brick on top of half-brick, except for Benei Haman and the kings of Eretz Yisrael, which are brick over brick and half-brick over half-brick.

Question: What is the reason?

Answer: This is so there will be no Tekumah (rise) after their fall.

Rishonim

The Rif and Rosh (1:9) bring our Gemara.

Rosh: Some say that one must stretch out the Kri'ah of the Vov (say it slowly). Some say that it must be written elongated. It is in the tradition of big letters.

Ran (DH Vov): The Vov is not listed in the tradition of big letters. One need not elongate it more than a regular Vov; rather, its head is straight. Alternatively, one stretches out the Kri'ah.

Ran (DH Kol): Rashi says that half-brick refers to the writing, and brick refers to the blank part. R. Tam says that both of them refer to writing; the bricks contain more writing than the half-bricks. The names of Benei Haman are the bricks, and the half-bricks are the words 'v'Es'. One cannot add to something built in this way (without protrusions) to stabilize it - this is the meaning of 'there is no Tekumah for their fall.' Shiras Ha'azinu is written similarly for it also discusses the fall of Resha'im. It contains only full bricks, therefore our Gemara did not mention it.

Rambam (Hilchos Megilah 2:12): One must say the 10 sons of Haman and "v'Aseres" in one breath to publicize that they were hung and killed like one.

Magid Mishnah: The Rif mentions stretching the 'Vov' of "Vayzasa" and writing this Shirah brick over brick and half-brick over half-brick. It is not clear why the Rambam omits these. Perhaps he had a different text in the Gemara.

Note: Perhaps the 'Vov' was not among the Rambam's tradition of big letters, and he sought an explanation for this. 'They were hung and killed' suggests that they died through hanging. This is unlike Rashi (Esther 9:13), who says that they hung the 10 sons who were killed on the 13th. Perhaps the Rambam learns from Rav (15b) who says that 10 sons of Haman died (on the 13th), 10 (i.e. others) were hung, and 10 begged for bread. Targum Sheni (9:14) explains that each hung from (the feet of) the one above. One would expect the top sons to die first. Perhaps 'they were hung and killed like one' means 'hanging from each other', but not at the same moment. We learn this from reading their names in one breath, so we need not elongate the Vov to teach this. Alternatively, 'like one' means the same moment; perhaps it was a miracle. Alternatively, Rav Ada holds that they were hung on separate scaffolds, unlike R. Yochanan and Targum Sheni, and the Rambam rules like Rav Ada.

Poskim

Shulchan Aruch (OC 690:15): One must say the 10 sons of Haman and "v'Aseres" in one breath to publicize that they were killed and hung together.

Rema: This is l'Chatchilah. If one paused in the middle he was Yotzei. L'Chatchilah the custom is to say them all in one breath, starting from "Chamesh Me'os Ish" and ending with "Aseres".

Gra (DH ul'Chatchilah): Hagahos Maimoniyos (2:1) questions why we start from "Chamesh Me'os Ish". We say the 10 sons in one breath because they died at the same time. This does not apply to the 500 people! Rav Yitzchak ben Yehudah says not to pause between verses, even to breathe, because it is called Igeres; some have this custom. However, to fulfill this it suffices to start from "Ish". Perhaps we start from "Chamesh" because Chamesh Me'os Ish is one matter. Rav Tzemach Gaon permits to pause in any place except for where Chachamim said not to.

Beis Yosef (DH l'Rebbi): The Gemara (21b) connotes that they used to translate between verses, unlike our custom not to pause between verses.

Magen Avraham (17): One should not delay more than the time needed to breathe, even between verses, because it is called Igeres.

Ma'amar Mordechai (10), brought in Hagahos Tur ha'Shalem (17): The Ibn Ezra (Esther 9:27) says that in Megilas Esther we pause only between verses (this is our text of the Ibn Ezra, unlike the Beis Yosef's text). This is because Ezra enacted pauses (in all of Tanach) very soon after the Megilah was written. However, most of Tanach was written long before Ezra, and people were already used to pausing in other places.

Mishnah Berurah (54): The Gemara requires only the 10 sons in one breath. Therefore, if one thinks that he cannot finish them if he starts from "Chamesh Me'os Ish", he should begin from "v'Es Parshandasa". B'Di'eved one is Yotzei even if he paused long enough to say everything (as long as there was no Halachic necessity to pause).

Kaf ha'Chayim (97): Some, amidst hurry to read the names in one breath, say 'v'Es' by heart. This is a mistake; every word must be read from the Megilah.

Shulchan Aruch (691:3): The 10 sons of Haman are written like a Shirah. It is unlike other Shiros in which blank stretches are over writing; rather, one leaves blank space between the writing. If this was not done it is Pasul.

Mishnah Berurah (17): The blank space must be twice the size of the writing. (Sha'ar ha'Tziyon 13 - this is like Rashi.)

Note: The Mishnah Berurah did not explain whether the blank space must be twice the size of the names of the 10 sons of Haman, or of the words ''v'Es", or both. Surely "v'Es" occupies less width than the names, which have up to seven letters (Parshandasa). Presumably the name and 'v'Es' (on the next line) together are considered a half brick. The same applies to Shiras ha'Yam, in which alternative lines have only one word at the beginning and one at the end.

Shulchan Aruch (ibid. 4): One must lengthen the 'Vov' of "Vayzasa".

Rema: It should be written longer than normal. Some say that one elongates its pronunciation.