An interesting but little-used form of the abacus was developed by Gerbert, who later (in 999) became Pope Sylvester II. This contained twenty-seven columns; in each column just one marked counter would be placed-for example, a counter with some form of the numeral 4 on it would be used instead of four actual counters. The counters were called apices ; there was no zero counter, however. The physical assistance of the actual number of counters was lost in this abacus, and it never became popular.