What's the difference between altar and piscina?

Altar

Definition:

(n.) A raised structure (as a square or oblong erection of stone or wood) on which sacrifices are offered or incense burned to a deity.
(n.) In the Christian church, a construction of stone, wood, or other material for the celebration of the Holy Eucharist; the communion table.

Example Sentences:

(1) From Africa, the archbishop of Kenya warned "the devil has entered the church", while a few days before the ceremony Robinson received a postcard from England, depicting the high altar of Durham cathedral and bearing the message: "You fornicating, lecherous pig."
(2) In its proposals the MoJ is displaying a callous disregard for the rights of its citizens, as client choice and quality of legal service have been sacrificed on the altar of price competition.
(3) Because of course nothing is more destructive of the sanctity of his own vocation than the suggestion that we simply don't need this kind of conservation – if that's what it really is – at all; that on the contrary, the entire "relaunch" is simply the bastard offspring of an orgiastic union between Mammon and science, consummated on the Stonehenge altar stone and observed by the fee-paying public.
(4) He thought he would be his altar boy but it turned out that Ahmadinejad wanted to be the priest."
(5) From glossy magazines to giant billboards and the celebrity culture we obsessively consume, all kneel at the altar of the airbrushed.
(6) His bedridden mother stumbled to her feet Tuesday to pray at the altar set up where he slept.
(7) Facebook Twitter Pinterest People pray in front of an altar especially set up Tama’s funeral in Kinokawa City, Wakayama prefecture.
(8) During the original trial, much emphasis was placed on the blasphemy of the women doing their dance right in front of the altar.
(9) The volte face was a result of Russian blackmail, the Lithuanian president's office said as senior officials in Brussels said Yanukovych was sacrificing the hopes and wishes of most of his countrymen on the altar of Russian money and contracts.
(10) Because by then I had learned, rubbing polish into an altar, that active citizenship is essential for any functioning democracy.
(11) Economics is thus humiliated on the altar of politics, and principle is sacrificed to expediency.
(12) Dr David Petts, a lecturer in archaeology at Durham University, said: "We found the Binchester head close to where a small Roman altar was found two years ago.
(13) How dangerously flimsy would one's marriage have to be before it felt threatened by other couples signing a different piece of paper – or, indeed, by a same sex couple following you to the altar?
(14) If a rock group invaded Westminster Abbey and gravely insulted a religious or ethnic minority before the high altar, we all know that ministers would howl for "exemplary punishment" and judges would oblige.
(15) The temple originally had a sunken nave flanked by seven symbolic pairs of pillars leading to the altar, a ritual well and raised seating on either side.
(16) In a country where voters do not want to sacrifice social welfare to the altar of austerity, analysts warn none of the main candidates are going far enough to slash spending.
(17) Though the Queen will not wear St Edward's crown, the heavy gold crown first used for Charles II's coronation, at Tuesday's service, it will be brought from its home at the Tower of London to rest on the abbey's high altar, along with the Ampulla, the hollow gold eagle from which oil was poured to anoint her in 1953.
(18) When the Dalai Lama came to collect his cheque at a ceremony in St Paul's Cathedral, eight Buddhist monks sat chanting in front of the high altar as the nave filled up.
(19) Dominique Venner , 78, a far-right essayist and historian took his life in front of the altar at Notre Dame on Tuesday after writing a blog condemning France's recently passed law allowing same-sex marriage and adoption.
(20) "Don't tell me that this Compeyson is the man who left Miss Havisham at the altar, that he is now searching for you in London, and that you are actually Estella's father."