The poem "Death the Leveller" contains a line at the end of the poem which states:
Upon Death's purple alter now.
The reference to the color purple is very important in this line given the meaning behind the use of the color. The color purple can represent many different things. First, it is made from combining the colors red (the warmest color) and blue (the coolest color). This makes purple a color which holds balance.
The color purple is also a color typically used in religious ceremonies given its historical use in being worn by both royalty and is used as the color most representative by the Catholic Church during Advent. Purple is also the color used in funerals.
Given that the poem has a religious undertone, as denoted by the term 'alter', the use of the color purple makes sense.
As for the meaning of the line "Upon Death's purple alter now", the line refers to the fact that no one can escape Death. Death, in this case, is personified. What this means is that death is given a proper name (Death- denoted by the capitalization) and, therefore, is able to function in the same way that man can (Death can "lay his icy hand on kings").
Simplistically, what is being said is that all men will come to lie on Death's alter- a place where all who die must come.