In the

United States Court of Appeals

For the Seventh Circuit

No. 01-2522

Santiago V. Marques and Carey Portman,

Plaintiffs-Appellants,

v.

Federal Reserve Bank of Chicago

and Unknown Shareholders of the

Federal Reserve Bank of Chicago,

Defendants-Appellees,

and

Federal Deposit Insurance Corporation,

Defendant.

Appeal from the United States District Court

for the Northern District of Illinois, Eastern Division.

No. 00 C 5646--Harry D. Leinenweber, Judge.

Argued March 6, 2002--Decided April 16, 2002

 Before Posner, Evans, and Williams, Circuit

Judges.

 Posner, Circuit Judge. The plaintiffs

brought suit against the Federal Reserve

Bank of Chicago and the Federal Deposit

Insurance Corporation, plus the

shareholders of the federal reserve bank

(the other national banks in the bank’s

federal reserve district, 12 U.S.C.

sec.sec. 222, 282; Lewis v. United

States, 680 F.2d 1239, 1241 (9th Cir.

1982)), which are individually liable for

the bank’s debts "to the extent of the

amount of their subscriptions to [the

bank’s] stock at the par value thereof in

addition to the amount subscribed." 12

U.S.C. sec. 502. The plaintiffs claim to

be the agents for the owners of $25

billion in bearer bonds that the bank had

issued back in 1934 in exchange for 1665

metric tons of gold. They want the bank

ordered to redeem the bonds for face

value plus simple interest at 4 percent

since 1934 (although the bonds matured in

1965); the total amount of money they are

seeking is thus close to $100 billion.
 The suit is preposterous. There is no

record of any such bond issue, and as the

national debt of the United States was

only $28 billion in 1934, as a year later

the entire stock of gold owned by the

United States had a value of only $9

billion, and as no securities issue by a

U.S. government entity exceeded $100

million before 1940, the claim that in

1934 a federal reserve bank issued bonds

that virtually doubled the national debt

and added $25 billion in gold to the

government’s gold holdings can only cause

one to laugh. What is more (not that more

is needed), although the price at which

the government bought gold was fixed at

$35 an ounce effective at the beginning

of that year, the plaintiffs are claiming

that the federal reserve bank bought gold

from their predecessors at a price of

$467.02 an ounce. The plaintiffs further

undermine their case by arguing that

there is an international conspiracy to

deny the validity of these bonds, a

conspiracy pursuant to which the

plaintiffs’ documents expert, who

certified the genuineness of the bonds

(in an unsworn and evasive report), has

been repeatedly arrested and then

released without charges being filed.

 The bank’s lawyer told us without being

contradicted that the Department of

Justice has declined to prosecute

thepersons involved in the fraud because

no one could possibly be deceived by such

obvious nonsense. We are puzzled by this

suggestion. The Treasury has established

a Website warning the public against the

class of frauds (called "Morgenthaus,"

after Henry Morgenthau, Jr., the

Secretary of the Treasury in 1934) of

which the bond issue alleged in this suit

is one (the others also involve supposed

$25 billion bond issues). See

http://www.publicdebt.treas.gov/cc/

ccphony3.htm. There is no ceiling on

gullibility. Mr. Portman, the plaintiff

who argued the appeal pro se, is one of

the deceived--if he is not one of the

deceivers, another and perhaps more

plausible possibility, Portman having re

cently submitted a demand to the Federal

Reserve Bank of Cleveland that it pay

him $125 billion to redeem a similar set

of fictitious 1934-vintage "Federal

Reserve Bonds." We are sending this

opinion to the Justice Department for

whatever further consideration the
Department may wish to give the fraud.

 But though the suit is absurd, the

appeal, from the denial of the

plaintiffs’ Rule 60(b) motion to vacate

the judgment that the district court

entered in response to the bank’s motion

for summary judgment, is not. The

plaintiffs attempted to dismiss their

suit voluntarily under Fed. R. Civ. P.

41(a)(1). Had they succeeded in their

attempt, the dismissal would have been

without prejudice, and so they could

reinstate the suit without facing the bar

of res judicata. They can’t do that if

the judgment granting the bank’s motion

for summary judgment--a judgment on the

merits and therefore with prejudice--

stands.

 The reason they give for having wanted

to dismiss their suit is, naturally,

preposterous--that they were in serious

negotiations in Spain with the U.S.

Government and hoped that the government

would acknowledge the legitimacy of their

claim so that they could sell the bonds

to Russia. But one doesn’t need a good

reason, or even a sane or any reason, to

dismiss a suit voluntarily. The right is

absolute, as Rule 41(a)(1) and the cases

interpreting it make clear, Commercial

Space Mgmt. Co. v. Boeing Co., 193 F.3d

1074, 1077 (9th Cir. 1999); Marex

Titanic, Inc. v. The Wrecked & Abandoned

Vessel, 2 F.3d 544, 546 (4th Cir. 1993);

Eastalco Aluminum Co. v. United States,

995 F.2d 201, 204 (Fed. Cir. 1993);

Matthews v. Gaither, 902 F.2d 877, 880

(11th Cir. 1990) (per curiam), until, as

the rule states, the defendant serves an

answer or a motion for summary judgment.

The plaintiffs filed their notice of

voluntary dismissal, and the bank served

a motion to dismiss the suit under Rule

12(b)(6), on the same day. A motion under

Rule 12(b)(6) becomes a motion for

summary judgment when the defendant

attaches materials outside the complaint,

as the bank did, and the court "actually

considers" some or all of those

materials. Berthold Types Ltd. v. Adobe

Systems Inc., 242 F.3d 772, 775-76 (7th

Cir. 2001); see also State ex rel. Nixon

v. Coeur D’Alene Tribe, 164 F.3d 1102,

1107 (8th Cir. 1999); Finley Lines Joint

Protective Bd. Unit 200 v. Norfolk

Southern Corp., 109 F.3d 993, 997 (4th

Cir. 1997); Aamot v. Kassel, 1 F.3d 441,

444 (6th Cir. 1993) ("conversion [from a
Rule 12(b)(6) motion to a summary

judgment motion] takes place at the

discretion of the court, and at the time

the court affirmatively decides not to

exclude the extraneous matters"); Garita

Hotel Limited Partnership v. Ponce

Federal Bank, F.S.B., 958 F.2d 15, 18

(1st Cir. 1992); 9 Charles Alan Wright &

Arthur R. Miller, Federal Practice and

Procedure sec. 2363 (2d ed. 1995). But

the judge did not convert the bank’s

motion to a motion for summary judgment

until later.

 And anyway we do not know which

document, the plaintiffs’ notice of

voluntary dismissal or the defendant’s

motion to dismiss, was filed first. The

plaintiffs argue that the bank

acknowledged in the district court that

the notice of voluntary dismissal was

filed before the motion for summary

judgment was served, but the only record

of this acknowledgment is a transcript

that the parties neglected to make a part

of the appellate record. However, the

district judge, rather than make a

finding on which document came first,

appears to have believed that as long as

they were on the same day, it didn’t

matter which came first. (It is

unquestioned that the plaintiffs did

succeed in dismissing the FDIC as a

defendant under Rule 41(a)(1), and it is

not a party to this appeal.) We cannot

find an appellate case on who has the

burden of proving the sequence of the

filings, but Keal v. Monarch Life Ins.

Co., 126 F.R.D. 567 (D. Kan. 1989),

places the burden on the defendant,

sensibly, as it seems to us, since it is

the defendant that is asserting the right

to prevent the plaintiff from dismissing

the suit.

 Both because the district judge did not

convert the motion to dismiss to a motion

for summary judgment before the

plaintiffs filed their Rule 41(a)(1)

notice and because the defendant failed

to show that its motion was served before

the plaintiffs’ notice, were the appeal

from the judgment in favor of the bank it

would be clear that we would have to

vacate the judgment and remand the case

to the district court with directions to

permit dismissal under that rule. But we

must consider the bearing of the fact

that the appeal is not from the judgment,

but rather from the denial of a Rule
60(b) motion to vacate the judgment. A

legal error by the district court is not

one of the specified grounds for such a

motion. In fact it is a forbidden ground,

Russell v. Delco Remy Division, 51 F.3d

746, 749 (7th Cir. 1995), because if

permitted it would enable a losing party

to appeal outside the time limits for

appeals without excuse, since the

existence of the error would be apparent

from the district court’s judgment and

thus could be corrected on appeal within

the time allowed for taking an appeal.

Bell v. Eastman Kodak Co., 214 F.3d 798,

801 (7th Cir. 2000); Neuberg v. Michael

Reese Hospital Foundation, 123 F.3d 951,

955 (7th Cir. 1997); Bank of California,

N.A. v. Arthur Andersen & Co., 709 F.2d

1174, 1176-77 (7th Cir. 1983); Hess v.

Cockrell, 281 F.3d 212, 216 (5th Cir.

2002); Plotkin v. Pacific Telephone &

Telegraph Co., 688 F.2d 1291, 1293 (9th

Cir. 1982).

 However, the fourth subsection of Rule

60(b) authorizes a void judgment to be

vacated. As an original matter, we might

doubt whether an error that results in

denying a plaintiff his right of

voluntary dismissal is so fundamental or

grave that it should be treated as void,

implying that the judgment could be

vacated many years after it had been

entered even though the error that had

made it invalid when entered had not been

called to the judge’s attention in a

timely fashion. Rule 60(b)(4) is

primarily intended for cases where the

suit in which the judgment sought to be

vacated was entered was outside the

jurisdiction of the district court, as in

Pacurar v. Hernly, 611 F.2d 179 (7th Cir.

1979); see also United States v. Zima,

766 F.2d 1153, 1159 (7th Cir. 1985),

which this suit was not.

 There is, however, considerable and

unchallenged case authority (including

decisions by this court) that a judgment

on the merits that is entered after the

plaintiff has filed a proper Rule

41(a)(1) notice of dismissal is indeed

void. E.g., Beck v. Caterpillar Inc., 50

F.3d 405, 407 (7th Cir. 1995); Bryan v.

Smith, 174 F.2d 212, 214-15 (7th Cir.

1949); Duke Energy Trading & Marketing,

L.L.C. v. Davis, 267 F.3d 1042, 1049 (9th

Cir. 2001); American Soccer Co. v. Score

First Enterprises, 187 F.3d 1108, 1112

(9th Cir. 1999); Bonneville Associates,
Limited Partnership v. Barram, 165 F.3d

1360, 1364 (Fed. Cir. 1999); Meinecke v.

H & R Block, 66 F.3d 77, 82 (5th Cir.

1995) (per curiam); Safeguard Business

Systems, Inc. v. Hoeffel, 907 F.2d 861,

864 (8th Cir. 1990); Foss v. Federal

Intermediate Credit Bank, 808 F.2d 657,

660 (8th Cir. 1986); Williams v. Ezell,

531 F.2d 1261, 1264 (5th Cir. 1976). The

cases further make clear that although

not every "void" judgment is subject to

collateral attack, only those where the

voidness is unarguable, In re Edwards,

962 F.2d 641, 644 (7th Cir. 1992), the

refusal to vacate under Rule 60(b)(4) an

unarguably void judgment is an abuse of

discretion. Robinson Engineering Co.,

Ltd. Pension Plan & Trust v. George, 223

F.3d 445, 448 (7th Cir. 2000); Blaney v.

West, 209 F.3d 1027, 1031 (7th Cir.

2000); United States v. Indoor

Cultivation Equipment From High Tech

Indoor Garden Supply, 55 F.3d 1311, 1317

(7th Cir. 1995); see generally Hertz

Corp. v. Alamo Rent-A-Car, Inc., 16 F.3d

1126, 1130 (11th Cir. 1994); Williams v.

Brooks, 996 F.2d 728, 730 (5th Cir. 1993)

(per curiam); Jalapeno Property

Management, LLC v. Dukas, 265 F.3d 506,

515-16 (6th Cir. 2001) (concurring

opinion).

 We are therefore compelled to reverse

the judgment and direct the dismissal of

the suit, without prejudice, under Rule

41(a)(1). Should the plaintiffs attempt

to bring a new suit similar to the one

they are dismissing, namely a fraudulent

and possibly a criminal suit, they will

be subject to appropriate sanctions.

Reversed.