Read here and here. Map source here. A peer-reviewed study utilizing high resolution data from a peat bog sediment core, analyzes 6,000 years worth of a temperature proxy. The researchers determined that both Roman and Medieval Periods experienced temperatures that were significantly higher than those of the current period. (click on image to enalrge)
"Working with cores extracted from a peat bog west of Jinchuan, China the authors developed "a 6000-year high-resolution δ18O record of peat plant cellulose," which they interpret as "reflecting changes in regional surface air temperature." And from their results, which are depicted in the figure [adjacent], it can be seen that the Medieval Warm Period (which was preceded by the Dark Ages Cold Period and followed by the Little Ice Age) was considerably warmer than the Current Warm Period (which followed the Little Ice Age) has been to date"
Additional climate history postings. Historical temperature charts.