Many scholars point to the decreasing yield spread between the benchmark German bund and other European states as a sign of unprecedented European integration since Maastricht. There are two possible issues with this claim. First, without a historical perspective on sovereign bond yields and their comovements, researchers cannot determine how current levels of integration compare to previous periods of European history. To my knowledge, no previous research examines European yields from the formation of the ECSC or EEC to present, let alone pre-war spreads. Second, the first two moments of yield spreads do not necessarily capture meaningful integration. While the spreads are certainly an important measure, we can better assess integration by examining the correlation of these yields. In this article, I address both of these issues as follows. First, I describe an alternative method of measuring integration in the sovereign bond market based on an eigendecomposition of the time-dependent correlation of yields and their first-order differences [...]