The Torah ark or ark in a synagogue (Jewish house of worship) is known in Hebrew as the Aron Kodesh by the Ashkenazim and as the Hekhál amongst most Sefardim. It is generally a receptacle, or ornamental closet, which contains each synagogue's Torah scrolls (Sifrei Torah in Hebrew). In most cases, when possible, the ark is located on the wall of the synagogue closest to Jerusalem.
Origin of the names 
Aron Kodesh 
Aron Kodesh comes from Hebrew אָרוֹן קׄדֶש ʼārōn qōdeš (i.e. aron kodesh), Holy Ark. This name is a reference to the ’ārōn haqqōdeš, the Hebrew name for the Ark of the Covenant which was stored in the Holy of Holies in the ancient Tabernacle and the Temple in Jerusalem.
Hekhál, also written hechal, echal or heichal — and sometimes also Echal Kodesh (mainly amongst Balkan Sephardim) comes from Hebrew הֵיכָל [hēkhāl] ‘palace’, a term which was also used in the time of the Temple in Jerusalem to refer to the inner sanctuary containing the Holy of Holies. The hekhal contained the Menorah, Altar of Incense, and Table of the Showbread.
Placement and structure 
The ark is usually placed on or near that wall of the sanctuary which is facing Jerusalem — in practice often on the East wall, even in many cases where this is not in the direction of Jerusalem, and in some cases also on a seemingly random wall which was seen as architecturally easiest when the synagogue was constructed. In those cases where the ark does not show the direction to Jerusalem, traditional Judaism instructs the worshipper to face the true direction towards Jerusalem in prayers like the Amidah.
In some ancient synagogues, such as the fifth-century synagogue in Susia, the Torah scroll was not placed inside the synagogue at all, but in a room adjacent to it, showing that the sacredness of the synagogue does not come from the ark but from its being a house of prayer. The Torah was brought in to the synagogue for reading.
Most arks feature a parokhet (curtain). The parokhet can be placed outside the doors of the ark (typical Ashkenazi and Mizrachi custom) or inside the doors of the ark (typical Spanish and Portuguese and Moroccan Sephardi custom).
Some arks are built around a steel safe, which protects the Torah scrolls from fire or theft. Typically, the safe features a combination lock.
See also 
- Transliterated Hebrew Glossary. Derech.org
- The Israel Koschitzky Virtual Beit Midrash. Yeshivat Har Etzion
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