PISCINA, a Latin word first applied to a fish-pond, and later used for any pool of water for bathing, etc., either natural or artificial, and also for a tank or reservoir. In ecclesiastical usage the term was given to a shallow stone basin (the French cuvette) placed near the altar in a church, with drains to take away the water used in the ablutions at the mass. " Piscinae " seem at first to have been mere cups or small basins, supported on perforated stems, placed close to the wall, and afterwards to have been recessed therein and covered with niche heads, which often contained shelves to serve as aumbries. They are rare in England till the 13th century, after which there is scarcely an altar without one. They frequently take the form of a double niche, with a shaft between the arched heads, which are often filled with elaborate tracing.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)