Maryland Constitution of 1867 Art. 11-E, § 2

The General Assembly, by law, shall classify all such municipal corporations by grouping them into not more than four classes based on population as determined by the most recent census made under the authority of the United States or the State of Maryland. No more than one such grouping of municipal corporations into four (or fewer) classes shall be in effect at any time, and the enactment of any such grouping of municipal corporations into four (or fewer) classes shall repeal any such grouping of municipal corporations into four (or fewer) classes then in effect. Municipal corporations shall be classified only as provided in this section and not otherwise.