SC 13G/A

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G

Under the Securities Exchange Act of 1934
(Amendment No. 2)*

ARCH CAPITAL GROUP LTD.

(Name of Issuer)

Common Stock $.01 par value per share

(Title of Class of Securities)

G0450A105

(CUSIP Number)

March 6, 2006

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

o	Rule 13d-1(b)
ý	Rule 13d-1(c)
o	Rule 13d-1(d)

*The remainder of this cover page shall be filled out for a reporting person's initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter the disclosures provided in a prior cover page.

The information required in the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

CUSIP No. G0450A105
	1.	Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only) Cascade Investment, L.L.C.
	2.	Check the Appropriate Box if a Member of a Group (See Instructions)
		(a)		o
		(b)		o
	3.	SEC Use Only
	4.	Citizenship or Place of Organization State of Washington
Number of Shares Beneficially Owned by Each Reporting Person With			5.		Sole Voting Power 2,368,653*
			6.		Shared Voting Power  -0-
			7.		Sole Dispositive Power  2,368,653*
			8.		Shared Dispositive Power -0-
	9.	Aggregate Amount Beneficially Owned by Each Reporting Person 2,368,653*
	10.	Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o
	11.	Percent of Class Represented by Amount in Row (9) 3.2%
	12.	Type of Reporting Person (See Instructions) OO

*  All shares held by Cascade may be deemed to be beneficially owned by William H. Gates III as the sole member of Cascade.

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CUSIP No. G0450A105
	1.	Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only) William H. Gates III
	2.	Check the Appropriate Box if a Member of a Group (See Instructions)
		(a)		o
		(b)		o
	3.	SEC Use Only
	4.	Citizenship or Place of Organization United States of America
Number of Shares Beneficially Owned by Each Reporting Person With			5.		Sole Voting Power 2,368,653*
			6.		Shared Voting Power  -0-
			7.		Sole Dispositive Power  2,368,653*
			8.		Shared Dispositive Power -0-
	9.	Aggregate Amount Beneficially Owned by Each Reporting Person 2,368,653*
	10.	Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o
	11.	Percent of Class Represented by Amount in Row (9) 3.2%
	12.	Type of Reporting Person (See Instructions) IN

*  All shares held by Cascade may be deemed to be beneficially owned by William H. Gates III as the sole member of Cascade.

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EXPLANATORY STATEMENT

This Amendment No. 2 on Schedule 13G is being filed to report that as a result of the issuance by Arch Capital Group Ltd. (the “Issuer”) of additional shares of its Common Stock, $.01 par value per share (“Common Stock”), upon the conversion of the Issuer’s series A convertible preference shares in December 2005 by the holders thereof, the Reporting Persons are now the beneficial holders of less than 5% of the total Common Stock outstanding.

Item 1.
	(a)	Name of Issuer Arch Capital Group Ltd.
	(b)	Address of Issuer’s Principal Executive Offices Wessex House, 45 Reid Street, Hamilton HM 12, Bermuda
Item 2.
	(a)	Name of Person Filing (1)  Cascade Investment, L.L.C. (“Cascade”) (2)  William H. Gates III
	(b)	Address of Principal Business Office or, if none, Residence (1)  2365 Carillon Point, Kirkland, Washington 98033 (2)  One Microsoft Way, Redmond, Washington 98052
	(c)	Citizenship (1)  Cascade is a limited liability company organized under the laws of the State of Washington. (2)  William H. Gates III is a citizen of the United States of America.
	(d)	Title of Class of Securities Common Stock, $.01 par value per share
	(e)	CUSIP Number G0450A105
Item 3.	If this statement is filed pursuant to §§240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
	(a)	o	Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o).
	(b)	o	Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c).
	(c)	o	Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c).
	(d)	o	Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C 80a-8).
	(e)	o	An investment adviser in accordance with §240.13d-1(b)(1)(ii)(E);
	(f)	o	An employee benefit plan or endowment fund in accordance with §240.13d-1(b)(1)(ii)(F);
	(g)	o	A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
	(h)	o	A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
	(i)	o	A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
	(j)	o	Group, in accordance with §240.13d-1(b)(1)(ii)(J).
	Not Applicable

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Item 4.	Ownership
Provide the following information regarding the aggregate number and percentage of the class of securities of the issuer identified in Item 1.
	(a)	Amount beneficially owned:    2,368,653*
	(b)	Percent of class:    3.2%
	(c)	Number of shares as to which the person has:
		(i)	Sole power to vote or to direct the vote    2,368,653*
		(ii)	Shared power to vote or to direct the vote     -0-
		(iii)	Sole power to dispose or to direct the disposition of    2,368,653*
		(iv)	Shared power to dispose or to direct the disposition of    -0-
		*      All shares held by Cascade may be deemed to be beneficially owned by William H. Gates III as the sole member of Cascade.
Item 5.	Ownership of Five Percent or Less of a Class
If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following   ý.
Item 6.	Ownership of More than Five Percent on Behalf of Another Person
Not Applicable
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company or Control Person
Not Applicable
Item 8.	Identification and Classification of Members of the Group
Not Applicable
Item 9.	Notice of Dissolution of Group
Not Applicable
Item 10.	Certification
	By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect.

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SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Date:  March 6, 2006
CASCADE INVESTMENT, L.L.C.
By	/s/ Michael Larson
	Michael Larson, Business Manager
WILLIAM H. GATES III
/s/ Michael Larson
William H. Gates III, by Michael Larson as attorney-in-fact*

JOINT FILING AGREEMENT

We, the signatories of the statement to which this Joint Filing Agreement is attached, hereby agree that such statement is filed, and any amendments thereto filed by either or both of us will be filed, on behalf of each of us.

DATED:  March 6, 2006

CASCADE INVESTMENT, L.L.C.
By:	/s/ Michael Larson
	Michael Larson, Business Manager
WILLIAM H. GATES III
/s/ Michael Larson
William H. Gates III, by Michael Larson as attorney-in-fact*

*  Duly authorized under Special Power of Attorney appointing Michael Larson attorney-in-fact, dated February 3, 2006, by and on behalf of William H. Gates III, attached hereto as Exhibit 99.1.

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EX-99.1

Exhibit 99.1

Special Power of Attorney

The undersigned does hereby constitute and appoint Michael Larson as the true and lawful attorney of the undersigned, with full power of substitution, and authorizes and designates him for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to execute, acknowledge, deliver and/or file any documents or filings and any amendments thereto made by or on behalf of the undersigned in respect of any securities held by the undersigned, directly, indirectly or beneficially or required in connection with the undersigned’s position as a director or officer of any entity under any laws of any pertinent jurisdiction or any relevant securities market or exchange. Without limitation, this authorization extends to and includes any questionnaires, required or discretionary reports and any and all documents and forms with any governmental office or agency, whether U.S., foreign, state or local (including, without limitation, the U.S. Securities & Exchange Commission and state securities administrators or commissions), any securities exchange or market (including, without limitation, the Nasdaq Stock Market), as may be required, or as the undersigned determines to be advisable, under applicable laws (including without limitation, the Securities Act of 1933, as amended, or the Securities Exchange Act of 1934, as amended, and rules and regulations under each of such laws), or rules and regulations of any securities exchange or market. The undersigned acknowledges that the foregoing attorney-in-fact, in serving in such capacity at the request of the undersigned, is not assuming any of the undersigned’s responsibilities to comply with such laws.

This Special Power of Attorney shall remain in full force and effect until withdrawn by the undersigned by written notice to the foregoing attorney-in-fact. This is a durable power of attorney and shall not be affected by the disability of the undersigned.

IN WITNESS WHEREOF, the undersigned has caused this Special Power of Attorney to be executed this 3rd day of February 2006.

	/s/ William H. Gates III
	William H. Gates III
/s Emily A. Byrne	/s/ Christine L. Turner
WITNESS	WITNESS

STATE OF WASHINGTON	)
	) ss.
COUNTY OF KING	)

I certify that I know or have satisfactory evidence that William H. Gates III is the person who appeared before me, and said person acknowledged that he signed this instrument as his free and voluntry act for the uses and purposes mentioned in the instrument.

	Dated:	February 3, 2006	/s/ Lorrie Paull
			Signature of Notary Public
[Seal or Stamp]			L. Paull
			Print Name
			My appointment expires	4.15.08