An abacus is denoted primarily a square tablet of any description, and was hence employed in the following significations: 1. A table, or side-board, chiefly used for the display of gold and silver cups, and other kinds of caluable and ornamental utensils. The use of abaci was first introduced at Rome from Asia Minor after the victories of Cn. Manlius Vulso, B.C. 187, and their introduction was regarded as one of the marks of the growing luxury of the age; 2. A draught-board or chess-board; 3. A board used by mathematicians for drawing diagrams, and by arithmeticians for the purposes of calculation; 4. In architecture, the flat square stone which constituted the highest member of a column, being placed immediately under te architrave.