Time series analysis for the Euro Area requires the availability of sufficiently long historical data series, but the appropriate construction methodology has received little attention. The benchmark dataset, developed by the European Central Bank for use in its Area Wide Model (AWM), is based on fixed-weight aggregation across countries with historically distinct monetary policies and financial markets of varying international importance. This paper proposes a new methodology, based on the historical distance from monetary integration between core and periphery countries, for producing back-dated monetary and financial series for the Euro Area. The impact of using the new methodology versus the AWM data is illustrated through a structural VAR analysis and estimates of an international DSGE model. An important advantage of the new methodology is that it can be applied to develop appropriate series as new member countries join the Euro Area.