The motion to quash the alternative writ is analogous to a demurrer in an ordinary action. The reasons stated for the motion may be treated as the reasons for a demurrer.
The charter of New Haven does provide that the city may carry out this order, and then recoup the expense from the railroad j that is one remedy open to the city, but it is not its only remedy. It might, in the name of the State upon its relation, compel obedience to the order by mandamus, because *48that order is a judgment. That would be the most effective way to secure obedience to this judgment; and it could not be denied this remedy because it could have done the work itself and sued for the expense incurred.
But there is not involved in this record any question of the remedies open to the city of New Haven. The city is not a party to this action. The State of Connecticut is the relator, seeking to secure obedience to. a judgment rendered by a member of one of her co-ordinate branches of government. State’s Attorney v. Branford, 59 Conn. 402, 408. This is her natural and only remedy. Indirectly the State might, perhaps, by contempt proceedings, have accomplished the same end; but mandamus by the State is the remedy to secure obedience to a judgment concerning a public matter. The first ground of the motion to quash is untenable.
The affirmance of the order of the court of common council by Judge Baldwin, was an adjudication by him upon appeal of the matters therein contained. Over parties and a matter within his jurisdiction, his adjudication has the same force and stands upon the same footing as a judgment of the Superior Court. This order adjudged that the order appealed from was valid and must be
This judgment may fairly be construed to have determined everything which the Act of 1897 commits to the railroad company, except that the Act of 1897 provides for the determination by the commissioners of a plan; and the order, upon a fair construction, provides that a bridge of a certain material, height, length and width shall be .built, and to the satisfaction of the board of public works. (So the question raised by this second ground is whether this statute is to be construed to apply to a case passed into judgment before its enactment; in other words, whether it is within the power of the legislature to practically vacate a final judgment by providing that the same matters therein adjudicated shall be again determined by another tribunal.]
The language of the Act does not expressly make it applicable to cases pending in court, much less to cases already adjudicated; and in the absences of express words or necessary implication it cannot be so construed.
*49There is a more potent reason for construing this statute as inapplicable to a case already gone into judgment. The construction claimed would vacate the judgment already had, and compel another adjudication of the same matter. (An Act of the legislature which opens or vacates a judgment is, generally speaking, void for two reasons: first, because it would impair the vested rights of him in whose favor the judgment ran; and second, because it would invade the judicial prerogative. J The first reason may not he of great weight in the particular case before us, since the successful litigant, the city of Hew Haven, may be said, as an agent of the State, to have no vested rights in an adjudication of this character which cannot be impaired at will by the power which created it. But the second reason is potential. (The separation of the powers of government into three departments, each of which within its own sphere is supreme, is a constitutional principle which cannot he overturned. The judgment is the final and supreme act of judicial power. The legislature cannot overturn judgments, any more than the judiciary can make laws. A judgment is based upon established rules and principles administered by the judiciary.
If the legislature can provide another tribunal to decide matters once decided by the judiciary, it could strip the judiciary of its functions, it could unsettle matters once determined, could substitute its will in place of settled principles of law, the growth of centuries, and it would in so doing destroy our system of government. The judgment of Judge Baldwin finally adjudicated the matters therein, and the legislature has not attempted to open or vacate that judgment, or retry through another tribunal the matters which Judge Baldwin tried and determined. Possibly it has no power to do so. Norwalk Street Ry. Co.’s Appeal, 69 Conn. 576; Denny v. Mattoon, 2 Allen, 361; Mayor, etc., v. Horn, 26 Md. 194, 206; Black on Judgments, § 298, and cases cited; 6 Amer. & Eng. Ency. of Law, (2d ed.) 1038, and cases cited; Hungerford’s Appeal from Probate, 41 Conn. 322, 327. The *50Act of 1897 cannot be construed so as to affect the present case.
The second and third reasons show no tenable ground for disturbing the judgment.
(The order of Judge Baldwin really passed upon only one matter. It decided that common convenience and necessity required an iron bridge to be built as ordered by the common council of New Haven, and that therefore the said order was not unreasonable or unjust, and that the defendant was not aggrieved. The determination of what constitutes common convenience and necessity is a judicial question.') Application of Shelton St. Ry. Co., 69 Conn. 627, and cases there cited.
Neither the fifth nor the sixth reason presents any question necessary to be considered.
There is no error.
In this opinion the other judges concurred.