1. The levying of a tax, whether general' or special, is an act of sovereignty, which the sovereign may not barter away.

2. A municipality in acquiring real estate for public purposes is not authorized to pay therefor more than its reasonable value. A covenant perpetually exempting real estate, other than acquired, from special assessments for all purposes, is a covenant running with the land, the reasonable value of which is un-ascertainable, and, therefore, affords no criterion whereby the value of the' consideration can be weighed against the reasonable value of the real estate acquired, and for that reason is ultra vires.

3. The exemption of certain real estate from special assessments necessarily results either in increasing the burden upon other real estate specially benefited or in depriving such other real estate of the benefit of needed improvements, thereby causing an unequal distribution of the burdens and benefits of government, and is both ultra vires and against public policy.

Judgment reversed.