``MASSIVE RELIC GALAXIES'' (MRGS) ARE LOCAL ANALOGS OF THE HIGH-REDSHIFT ``RED NUGGETS'' THOUGHT TO REPRESENT PROGENITORS OF TODAY'S EARLY-TYPE GALAXIES. MRGS BEING LOCATED AT LOW REDSHIFT ARE MUCH MORE ACCESSIBLE TO DETAILED OBSERVATIONAL STUDY. ANALYSIS OF A SHALLOW AO16 CHANDRA ACIS-S OBSERVATIONS OF THE MRG MRK 1216 REVEALS AN EXTENDED LUMINOUS HOT GAS HALO IMPLYING A MASSIVE GALAXY WITH M200 ~ (5-10) X 10^F12G MSUN. WE PROPOSE AN XMM-NEWTON OBSERVATION OF MRK 1216 TO MAP ITS GRAVITATING MASS PROFILE OUT TO A RADIUS R F2500G-R F500G AND OBTAIN PRECISE CONSTRAINTS (+/- 10%) ON THE HALO CONCENTRATION TOTAL MASS AND BARYON FRACTION THAT WILL REPRESENT THE FIRST SUCH MEASUREMENTS FOR AN MRG.