The submission in this case is plainly an attempt, on the part of the city of Somerville and of the owners of land taken for a new street in that city, to delegate to arbitrators chosen by the parties the power of determining the amount of the damages of the landowners, and of assessing the betterments or benefits received by the landowners by the laying out of the street, under the betterment laws, so called. The submission is peculiar, as it contains no covenants or stipulations on the part of the city, but the necessary implication is, that, upon performing the award based upon it, the parties are to be mutually released from all claims for damages and for betterments; other wise, there is no mutuality and no consideration for the promises of the parties of the second part.
The question which lies at the foundation of this case is, whether the city had' the power to enter into this agreement, for, if the execution of it by the city was ultra vires and void, the other parties would not be bound.
It is not necessary to decide whether, in a case where a way is laid out under the Gen. Sts. c. 43, the city or town has the power to submit to arbitration the question of the damages sustained by the landowner. In such a case, the controversy or question is between the town and each landowner separately, as to the damage he has sustained by the taking of his land; it concerns no one else, it may well be and often is settled by agreement, and it would seem that it might be referred to arbitrators as a convenient mode of settlement without affecting the rights of others or violating any principles of public policy. It was so held in Boston v. Brazer, 11 Mass. 447, under the laws as they then were. See Everett v. Charlestown, 12 Allen, 93 Campbell v. Upton, 113 Mass. 67.
But where a way is laid out under the betterment law, a dif* *275ferent ease is presented. Then it is the duty of the board of street commissioners or of aldermen in cities, and of selectmen in towns, to determine what real estate has received special benefit from the laying out, and to assess upon such estate a proportional share of the expense. This assessment is in the nature of a tax, which must be laid proportionally upon all the estates which are specially benefited. In laying it, the said boards act, not as agents of the city or town, but as public officers in a quasi judicial character. They are not subject to the direction or control of the city or town. The city or town cannot by any agreement abridge or limit the rights of the board, or exonerate an owner of benefited land from the liability to be assessed. Boylston Market Association v. Boston, 113 Mass. 528. Harvard College v. Boston, 104 Mass. 470. Brimmer v. Boston, 102 Mass. 19.
In the case at bar, therefore, the city of Somerville had no power to enter into an agreement to exonerate the persons who signed the submission as parties of the second part from liability to assessments for betterments. The submission was void, and the city cannot maintain an action to enforce the award made under it. Exceptions sustained