All taxes which may hereafter be lawfully imposed and assessed by counties, institution districts, cities, boroughs, towns, townships, and school districts on real property, are hereby declared to be a first lien on such real property (but subordinate to the lien of taxes imposed by the Commonwealth), and every such lien shall date from the day on which the millage or tax rate is fixed by the proper authority of any such political subdivision, except where such taxes are imposed and assessed prior to the commencement of the fiscal year for which the same are imposed or assessed, in which case the lien of such taxes shall date from the first day of the fiscal year for which such taxes are imposed or assessed.
53 P.S. § 7102