Pope Benedict XVI says Monday he will resign on February 28th because he no longer has the strength to fulfill the duties of his office, becoming the first pontiff since the Middle Ages to take such a step.

The 85-year-old pope said he believes his strength had deteriorated over recent months "to the extent that I have had to recognize my incapacity to adequately fulfill the ministry entrusted to me." A Vatican spokesman said the pontiff would step down from 1900 GMT on February 28, leaving the office vacant until a successor is chosen.

In doing so, he'll be the first pope in 600 years to leave office before passing away.  Only seven other popes have ever resigned in the history of the Catholic Church, though historical records from the earliest years of the church are very sketchy.  Benedict took office in 2005 after the passing of Pope John Paul II.