Which historical alkaline earth was used in ancient mortar?

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A color-coded periodic table of the elements displays each element's symbol and atomic number, with categories such as alkali metals, noble gases, halogens, transition metals, and actinoid elements distinguished by different background colors. — alkaline-earth metal Modern version of the periodic table of the elements (printable).

The earliest known alkaline earth used in ancient times was lime, which is now identified as calcium oxide. This substance was a key component in the composition of mortar used for construction.1

Historically, substances that were nonmetallic, insoluble in water, and resistant to fire were classified as "earths," and those that resembled alkalies were designated as alkaline earths. Lime, often obtained by calcining calcium carbonate such as limestone or shells, is a caustic solid that remains essential in the production of lime mortar and plaster.23