Ownership Submission
FORM 3
 UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940
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(Print or Type Responses)
1. Name and Address of Reporting Person *
  Lyons Mark Donald
 2. Date of Event Requiring Statement (Month/Day/Year)
05/03/2006		 3. Issuer Name and Ticker or Trading Symbol
ARCH CAPITAL GROUP LTD. [ACGL]
(Last)
(First)
(Middle)
ONE LIBERTY PLAZA, 53RD FLOOR		 4. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
_____ Director _____ 10% Owner
__X__ Officer (give title below) _____ Other (specify below)
COO Insur Gr. Operations
 5. If Amendment, Date Original Filed(Month/Day/Year)
(Street)

NEW YORK, NY 10006		 6. Individual or Joint/Group Filing(Check Applicable Line)
_X_ Form filed by One Reporting Person
___ Form filed by More than One Reporting Person
(City)
(State)
(Zip)
Table I - Non-Derivative Securities Beneficially Owned
1.Title of Security
(Instr. 4)		 2. Amount of Securities Beneficially Owned
(Instr. 4)		 3. Ownership Form: Direct (D) or Indirect (I)
(Instr. 5)		 4. Nature of Indirect Beneficial Ownership
(Instr. 5)
Common Shares, $.01 par value per share 32,023 (1)
D
 

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly. SEC 1473 (7-02)
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Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security
(Instr. 4)		 2. Date Exercisable and Expiration Date
(Month/Day/Year)		 3. Title and Amount of Securities Underlying Derivative Security
(Instr. 4)		 4. Conversion or Exercise Price of Derivative Security 5. Ownership Form of Derivative Security: Direct (D) or Indirect (I)
(Instr. 5)		 6. Nature of Indirect Beneficial Ownership
(Instr. 5)
Date Exercisable Expiration Date Title Amount or Number of Shares
Stock Option (right to buy)   (2) 08/06/2012 Common Shares, $.01 par value per share 18,116 $ 26.31 D  
Stock Option (right to buy)   (3) 09/22/2014 Common Shares, $.01 par value per share 28,000 $ 39 D  
Stock Option (right to buy)   (4) 02/23/2016 Common Shares, $.01 par value per share 20,000 $ 56.27 D  

Reporting Owners

Reporting Owner Name / Address Relationships
Director 10% Owner Officer Other
Lyons Mark Donald
ONE LIBERTY PLAZA, 53RD FLOOR
NEW YORK, NY 10006		       COO Insur Gr. Operations  

Signatures

/s/ Mark D. Lyons 05/05/2006
**Signature of Reporting Person Date

Explanation of Responses:

* If the form is filed by more than one reporting person, see Instruction 5(b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1) 962 of such shares are restricted and subject to vest on February 26, 2007; 1,666 of such shares are restricted and subject to vest on September 22, 2006 and 3,000 of such shares are restricted and subject to vest in three equal annual installments commencing on February 23, 2007.
(2) The stock options became exerciable in three equal annual installments commencing on August 6, 2002.
(3) The stock options became exerciable in three equal annual installments commencing on September 22, 2004.
(4) The stock option will become exercisable in three equal installments, with the first installment becoming exercisable on February 23, 2007 and the next two installments on February 23, 2008 and February 23, 2009.

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