The 9th c. B.C.E. Megaron 2 pebble mosaic from Gordion is the oldest known mosaic pavement to date. Discovered in 1956, it was subsequently cut into 33 individual panels, lifted, and stored outdoors for two decades before reinstallation under a sheltered, sub-grade, outdoor exhibit at the Gordion Museum. Recent research into its conservation history and current condition in preparation for re-interpretation and display has revealed the potential for further deterioration through alkali-silica reaction between the siliceous pebbles and the cementitious backing. Moreover, the enigmatic geometric designs are now difficult to read due to the loss of pebbles, misalignment of the panels, fragmentation by lacunae and gaps between the panels, rebar cracking, and cementitious over-grout. These conditions have created a critical situation that must be remedied to preserve this historically significant mosaic and make it more readily available for interpretation and exhibition. This paper assesses materials and techniques for re-backing the mosaic and investigates the potential for alkali-silica reaction. This includes empirical tests on replica mosaic panels for the removal of the reinforced concrete and cementitious over-grout, the evaluation of critical properties related to the facing and re-backing materials, and petrographic analysis for the detection of evidence of alkali-silica reaction. The analysis, testing, and proposed treatments for this significant archaeological pavement is presented in light of contemporary conservation approaches for ancient tessellated pavements and explores the limits to current knowledge and practice when applied to a natural pebble mosaics.