Mr. Justice Harris
delivered the opinion of the court.
Recapitulating the foregoing statement, this controversy presents a situation where the city passed appropriate ordinances for the widening of a street, charged all the costs to property within a prescribed assessment district, and apportioned $1,000 as the share of the expense of the improvements to be borne by two lots owned by Schmid; and subsequently in aid of the street improvement, the city commenced an action in the Circuit Court, under the general statutes, for the condemnation of a part of one of the lots owned by Schmid; the condemnation action resulted in a verdict and judgment allowing $8,000 as the damages “in excess of all benefits” to the two lots; and afterwards on appeal it was determined that the city was bound to pay Schmid $8,000 for the reason that the municipality had accepted the fruits of the judgment by taking possession of the condemned property; the city is attempting to deduct the assessments on the two lots from the $8,000 judgment while Schmid is endeavoring to compel the city to pay the judgment in full without making any deductions on account of the assessments against lots 1 and 2 in block 315. The theory of the municipality is that the Circuit Court was without *590jurisdiction to do more than ascertain the gross damages and that the judgment is void to the extent that it speaks of benefits. Schmid argues that the judgment is now final and conclusive and that the city is estopped from disputing the recitals found in it.
1, 2. A mandatory writ compelling the proper city officers to draw and deliver a warrant in payment of a judgment performs the office of an execution and, like most other proceedings to enforce a judgment, is usually collateral to the judgment sought to be enforced; and consequently the city cannot resist the writ by interposing all of the defenses and making all the objections that might have been available in the condemnation action. The attack now being made by the city is a collateral assault on the judgment rendered in the Circuit Court: 23 Cyc. 1064, 1346; 15 R. C. L., p. 874. A judgment which is void on its face may be collaterally attacked; but a party to a judgment cannot collaterally impeach it for errors of law or irregularities in practice which do no more than to render it merely erroneous or voidable: Morrill v. Morrill, 20 Or. 96, 105 (25 Pac. 362, 23 Am. St. Rep. 95, 11 L. R. A. 155); Smith v. Ormsby, 20 Wash. 396 (55 Pac. 570, 72 Am. St. Rep. 110); Edmundson v. Independent School District, 98 Iowa, 639 (67 N. W. 671, 60 Am. St. Rep. 224); Bear v. Board of County Commissioners, 122 N. C. 434 (29 S. E. 719, 65 Am. St. Rep. 711); Howard v. Huron, 5 S. D. 539 (59 N. W. 833, 26 L. R. A. 493); City of Sherman v. Langham, 92 Tex. 13 (40 S. W. 140, 42 S. W. 961, 39 L. R. A. 258); 23 Cyc. 1070, 1096. Quoting from 1 Black on Judgments (2 ed.), Section 246:
“If the judgment is void on its face it is of course a mere nullity and of no avail for any purpose, and this may be urged against it whenever it is brought in question. But otherwise, whether it be regular or irregu*591lar, correct or erroneous, valid or voidable, it is not subject to collateral attack.”
3. Subject to certain qualifications tbe general rule is tbat in a collateral proceeding a judgment imports verity and, as between the parties, is conclusive evidence of tbe facts recited in it: 23 Cyc. 855, 856; Boynton v. Crockett, 12 Okl. 57 (69 Pac. 869).
4. Tbe judgment in tbe condemnation action is not ambiguous but it measures up to tbe standard set by Dray v. Crich, 3 Or. 298, 299, 300, by stating in definite terms tbe matters tbat were adjudicated. Tbe language of tbe verdict and judgment is comprehensive, for both tbe jury and the court fix $8,000 as tbe “damages in excess of all benefits” to tbe two lots owned by Schmid.
5. It must be remembered tbat tbe city availed itself of tbe remedy offered by Sections 6859 to 6871, L. O. L., inclusive, for tbe condemnation of property for a public use; and tbat by tbe terms of Section 6864, L. O. L., tbe land owner may allege in bis answer “the true value of the lands and tbe damage resulting from tbe appropriation thereof”: Skelton v. Newberg, 76 Or. 126, 132 (148 Pac. 53). When tbe general statutes are resorted to for tbe condemnation of land for a public use tbe owner is entitled to allege and prove not only tbe value of tbe realty taken but also tbe damage to tbe remainder of tbe tract; and, ordinarily the appropriator may in turn offset tbe damages by showing that tbe remaining land is specially benefited, but the burden of showing special benefits is on tbe party seeking to condemn: 15 Cyc. 774; Portland & O. C. R. Co. v. Ladd Estate Co., 79 Or. 517, 520 (155 Pac. 1192); Beekman v. Jackson County, 18 Or. 283, 285 (22 Pac. 1074); Lamb v. Elizabeth City, 131 N. C. 241 (42 S. E. 603).
*5926. While special benefits allowed as an offset against damages in condemnation actions may differ in some respects from benefits assessed as betterments against property located within an improvement district nevertheless the right to levy local assessments is generally sustained on the theory that the assessed property is specially benefited by the improvement and therefore chargeable with the cost of the special benefit: Masters v. City of Portland, 24 Or. 161, 167 (33 Pac. 540); Oregon & Cal. R. Co. v. Portland, 25 Or. 229, 238 (35 Pac. 452, 22 L. R. A. 713); Ivanhoe v. City of Enterprise, 29 Or. 245, 248 (45 Pac. 771, 35 L. R. A. 58); King v. Portland, 38 Or. 402, 418 (63 Pac. 2, 55 L. R. A. 812); 1 Page and Jones on Tax. by Assessment, § 64; 15 Cyc. 561.
7. If the assessments levied upon lots 1 and 2 are deemed to be subsisting liens representing the amount of special benefits chargeable against the land then the verdict of the jury and the judgment of the court may fairly be construed to mean that the sum of the assessments plus all other benefits resulting from the street improvement were deducted from the gross damages and that the net damages amount to $8,000. This is the construction placed upon the verdict and judgment by the city in the appeal from the judgment in the condemnation action, for the city included among the assigned errors in that appeal a complaint because the court had received a verdict “which undertakes to make an award of damages ‘in excess of all benefits to lots 1 and 2, block 315 of the city of Portland’ ” and because the court had entered a judgment in conformity with the verdict; and, moreover, the city declared in its printed brief that “the verdict affects not only special benefits but all benefits.” The verdict and judgment therefore represent the net damages after *593deducting the local assessments and all other benefits. If the judgment represents the net damages then it necessarily follows that the city cannot again deduct the assessments for the reason that the benefits represented by the local assessments are chargeable but once: 1 Page and Jones on Tax. by Assessment, § 67; State ex rel. v. District Court, 66 Minn. 161 (68 N. W. 860); Davis v. Newark, 54 N. J. Law, 595 (25 Atl. 336).
8. Since the judgment is for the net damages after deducting the assessménts and all benefits the only inquiry remaining is whether the judgment is void or voidable. If the judgment is merely voidable then the collateral attack now made by the city must fail. The court had jurisdiction of the parties and of the subject matter. The very purpose of the litigation was to ascertain the compensation to be paid to Schmid for appropriating part of his land and in fixing the amount of compensation the court necessarily applied rules for measuring the compensation. These rules may have been correct or incorrect; if correct, the resultant of those rules is unassailable in any proceeding; and if incorrect, the resultant is safe from attack in a collateral proceeding even though it may be vulnerable to a direct assault. The court did exactly what it was called upon to do; it ascertained the compensation to be paid to Schmid. An incorrect measure of compensation would not necessarily render the judgment void because generally an incorrect measure would do no more than to render the judgment erroneous and voidable. While the verdict and judgment are unambiguous nevertheless if it were either necessary or proper to examine the complaint in the condemnation action that pleading might offer some explanation for the language of the verdict and judgment. The complaint tells about the $890 assessment on lot 1 and *594among the requests appearing in the prayer is one for permission to pay this and another lien out of the damages awarded by the jury. It is not necessary, nor do we attempt to decide whether Schmid was entitled to ignore the assessments and try the condemnation action as though no assessments had been levied, nor do we undertake to determine whether the city could have insisted on confining the jury to the single question of gross damages on the theory that the local assessments previously levied foreclosed the right of the Circuit Court to inquire into any benefits; but it is sufficient for the purposes of the instant case to say that the judgment in the condemnation action was not void but that it was either a perfect or merely an erroneous judgment. If on the one hand it is a perfect judgment it is impregnable; or if on the other hand it is merely erroneous but not void it is safe from attack for any of the reasons urged by the city in this collateral proceeding. Every blow attempted to be struck in this collateral attack against the condemnation judgment was also aimed at it when the city made a direct attack by appealing from the judgment. A judgment which has become a finality between Schmid and the City of Portland declares that $8,000 is the sum to be paid to the former “in excess of all benefits,” and as was said in Howard v. Huron, 5 S. D. 539 (59 N. W. 833, 26 L.R.A. 493):
“The judgment estops the city from asserting the fact to be otherwise. In theory of law, therefore, the assertion of the city cannot be true. ’ ’
Moreover, if the jury did deduct the assessments from the gross damages the municipality could not complain. Schmid is entitled to the unpaid balance of his judgment and his application for a peremptory writ of mandamus is granted. Writ Allowed.