The property of counties, cities and towns, owned and held only for public purposes, such as public buildings and the sites therefor, Fire engines and the furniture thereof, and all property used, or intended for extinguishing fires, public grounds and all other property devoted exclusively to the use and benifit† of the public shall be exempt from forced sale and from taxation, provided, nothing herein shall prevent the enforcement of the vendors lien, the mechanics or builders lien, or other liens now existing.