Sentence:  The interval of time supposed to have been denoted by the Roman <WSD>Lustrum</WSD> has been made the subject of controversy. No one however as far as we know has ever assumed it at less than four years or as more than five; so that the "status quæstionis" may so far be considered as fixed and agreed upon: and all that we have to do at present is to begin with inquiring whether the Roman <WSD>Lustrum</WSD> was more properly a period of five years or one of four. 
Meaning of the word marked with <WSD> tags:  A ceremonial purification of all the people, performed every five years after the taking of the census; a lustration. (from late 16th c.)