Kalasam

Hindu temples typically have Kalasam at the top of temple towers. These Kalasam in form of inverted pot is one of the prominent symbol of temples. Periodic renewal of temple is called kumbabishekam centers around Kalasams, when elaborate rituals are performed along with renewing the temple's physical structures.

Most Kalasam are made of metal and some of stone. View of Gopuram (Temple Tower) is one of the important rituals of Hindu worship along with view of Kodimaram (Temple flag mast). Elaborate Gopurams were built as worship of sky above, these Gopurams were topped with ornamental Kalasams.

Some temples have 4 entrance towers which protect about 75,000 sq meters on all four sides. However, this is approximate numbers.

Once in 12 years, the grains in the templekalasams are refilled and changed during a festival called “Kudamuzhugu Vilzha”.

Some people claim that this kalasam will act as a lightning conductor however there is no scientific basis for that claim. To prove that claim is wrong we can take the incident of breaking of kalasam at the Tanjore Big Temple due to lightning. This incident happened on November 28, 2010, When lightning hit one of the kalasams on "Rajarajan thiruvayil" it got damaged. By the way the "real" lightning conductor which was placed on the "Keralandhagan vayil" ( according to Archaeological Survey of India sources) helped to minimize the damage.

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Wikipedia