On a hill, far away, stood an old rugged cross...
This is basically a Latin Cross mounted on three steps. Calvaria (Latin), also known as Golgotha (Aramaic)1, is the name of a hill outside Jerusalem's gate and means "the place of a skull"2 - partly because it was a place of intense suffering, and partly because the skull-like appearance of the hillock.
In this symbol, the three steps leading up to the cross represent the hill of Calvary or, more often, in descending order they represent Faith, based upon Hope, based upon Love3.
The design is commonly seen as gravestones and is then referred to as a Stepped Cross. Each of the three plinth steps might have an epitaph inscribed, commemorating a deceased person or family buried there. (See also Grave Cross and Churchyard Cross.)
The steps are sometimes the base of a Table-top Cross or Altar Cross. As can be seen in ancient artwork, placing a cross and candles on the altar was not common until the 13th century. Before that, a cross may have been suspended from a canopy above the altar, and particles of the Host were arranged in the form of a cross. But it wasn't until about 800 years ago that pope Innocent III said "a cross is set upon the altar, in the middle between two candlesticks". At that time, it is probable that the cross was only placed on the altar during Mass.
Altar crosses or crucifixes now can be a permanent feature in Catholic, Lutheran and Anglican churches; less so in other Protestant churches. (Reformed and Anabaptist churches often refer to the altar as a 'communion table'.)
The Calvary Cross is often shown adorned with a cloth, draped over the cross-beam. (see Shrouded Cross)
See also Communion Cross.
A heraldic variation is a cross with steps (degrees, grieces) which could be on just the lower part, like a Calvary Cross, or on all four arms as shown in this example. Such a cross is referred to as a Degraded, Graded Cross or Croix Peronnée. There are often four steps and sometimes number as many as eight, diminishing in size as they ascend toward the centre.
The term degraded is not directly refering to the degradation suffered by Jesus on the cross, rather simply a pictorial description of the reducing sizes of the steps on each arm.
1 : John 19:17
2 : Matthew 27:33, Mark 15:22 and Luke 23:33
3 : 1 Corinthians 13:13