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                                                                    EXHIBIT 10.1

          LETTER OF CREDIT AND REIMBURSEMENT AGREEMENT AMENDMENT NO. 4

     This Letter of Credit and Reimbursement Agreement Amendment No. 4 dated as
of March 27, 2003 (this "AMENDMENT") is by and among Arch Reinsurance Ltd.
("REINSURANCE"), Arch Reinsurance Company ("ARCH COMPANY"), Alternative Re
Limited ("ALTERNATIVE"), Arch Insurance Company (formerly known as First
American Insurance Company) ("ARCH INSURANCE," and each of Reinsurance, Arch
Company, Alternative and Arch Insurance, individually, an "OBLIGOR" and
collectively, the "OBLIGORS") and Fleet National Bank (the "LENDER").

     PRELIMINARY STATEMENTS. The Obligors and the Lender entered into a Letter
of Credit and Reimbursement Agreement, dated as of April 17, 2002, as amended by
that certain Letter of Credit and Reimbursement Agreement Amendment No. 1 dated
as of November 4, 2002, as amended by that certain Letter of Credit and
Reimbursement Agreement Amendment No. 2 dated as of November 27, 2002, and as
further amended by that certain Letter of Credit and Reimbursement Agreement
Amendment No. 3 dated as of January 1, 2003 (as so amended, the "AGREEMENT").
The Obligors have requested that the Lender agree to extend the Facility
Termination Date from April 16, 2003 to July 14, 2003. The Lender is agreeable
to the Obligors' request subject to certain terms and conditions.

     Accordingly, the Obligors and the Lender agree as follows:

     Section 1. AMENDMENTS TO THE AGREEMENT: Effective as of the date hereof,
the Agreement is hereby amended as follows:

          (a)   The definition of "Facility Termination Date" set forth in
Section 1.1 of the Agreement is deleted in its entirety and the following is
substituted therefor:

                "FACILITY TERMINATION DATE" means July 14, 2003.

     Section 2. REPRESENTATIONS AND WARRANTIES OF THE OBLIGORS: In order to
induce the Lender to enter into this Amendment, each Obligor for itself hereby
represents and warrants that:

          (a)   Such Obligor (i) is a company or corporation duly organized,
validly existing without limitation of its corporate existence and in good
standing under the laws of its jurisdiction of organization and (ii) has
adequate power and authority and legal right to own or hold under lease the
properties it purports to own or to hold under lease and to carry on the
business in which it is engaged or presently proposes to engage. Such Obligor
has adequate power and authority to enter into this Amendment and to perform its
obligations under the Agreement as amended hereby.

          (b)   The execution and delivery by such Obligor of this Amendment and
the performance by such Obligor of its obligations in respect of the Agreement
as amended hereby have been duly authorized by all necessary corporate action on
the part of such Obligor and do not and will not (i) contravene any provision of
the Constituent Documents of such Obligor, (ii) conflict with, or result in a
breach of the terms, conditions or provisions of, or constitute a default

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under or, except as contemplated by the Agreement, result in the creation or
imposition of any Lien pursuant to the terms of any, mortgage, indenture, deed
of trust, security agreement, pledge agreement, charge or other instrument to
which such Obligor or any of its respective property is bound, (iii) violate any
law, governmental rule, regulation, order or decree of any court or
administrative agency or governmental officer applicable to and binding upon
such Obligor, (iv) require any waiver, consent or other action by any
governmental or regulatory authority or by any trustee or holder of any
Indebtedness or obligations of such Obligor or (v) require the approval of the
shareholders of such Obligor.

          (c)   This Amendment has been duly executed and delivered by such
Obligor and this Amendment and the Agreement as amended hereby constitutes a
valid and legally binding obligation of such Obligor enforceable in accordance
with its terms, except as such enforceability may be limited by (i) applicable
bankruptcy, insolvency, reorganization, moratorium, or other similar laws
affecting the enforcement of creditors' rights generally, and (ii) general
principles of equity (regardless of whether such enforceability is considered in
a proceeding in equity or at law).

          (d)   The Parent and such Obligor have heretofore furnished to the
Lender accurate and complete financial data and other information based on its
operations in previous years, and said financial data furnished to the Lender is
accurate and complete and fairly presents the financial position and the results
of operations for the period indicated therein.

          (e)   There has been no material adverse change in the condition,
financial or otherwise, of the Parent or such Obligor since the date of the most
recent financial statement and no Default or Event of Default exists with
respect to such Obligor.

          (f)   There are no legal or arbitral proceedings, or any proceedings
by or before any governmental or regulatory authority or agency, now pending or
(to the knowledge of such Obligor) threatened against the Parent or such Obligor
that are reasonably likely (either individually or in the aggregate) to have a
material adverse effect on the condition, financial or otherwise, of the Parent
or such Obligor.

          (g)   Such Obligor is in compliance with laws, regulations and orders
of any governmental agency or authority applicable to it or its Properties and
all indentures, agreements and other instruments binding upon it or its
Property, except where the failure to do so, individually or in the aggregate,
could not reasonably be expected to have a material adverse effect on its
condition, financial or otherwise.

     Section 3. REFERENCE TO AND EFFECT ON THE AGREEMENT.

          (a)   Upon the effectiveness of this Amendment, on and after the date
hereof, each reference in the Agreement to "this Agreement", "hereunder",
"hereof", "herein" or words of like import shall mean and be a reference to the
Agreement as amended hereby.

          (b)   Except as specifically amended above, the Agreement shall remain
in full force and effect and is hereby ratified and confirmed.

                                       -2-
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          (c)   The execution, delivery and effectiveness of this Amendment
shall not operate as a waiver of any right, power or remedy of the Lender under
the Agreement, nor constitute a waiver of any provision of the Agreement.

     Section 4. COSTS, EXPENSES AND TAXES. The Obligors agree to pay on demand
all reasonable costs and expenses of the Lender in connection with the
preparation, execution and delivery of this Amendment and any other instruments
and documents to be delivered hereunder, including, without limitation, the
reasonable fees and out-of-pocket expenses of counsel for the Lender with
respect thereto and with respect to advising the Lender as to its rights and
responsibilities hereunder and thereunder. In addition, the Obligors shall pay
any and all stamp and other taxes payable or determined to be payable in
connection with the execution and delivery of this Amendment and the other
instruments and documents to be delivered hereunder, and agree to save the
Lender harmless from and against any and all liabilities with respect to or
resulting from any delay in paying or omission to pay such taxes.

     Section 5. EXECUTION IN COUNTERPARTS. This Amendment may be executed in any
number of counterparts, each of which when so executed and delivered shall be
deemed to be an original and all of which taken together shall constitute but
one and the same instrument.

     Section 6. GOVERNING LAW. This Amendment shall be governed by, and
construed in accordance with, the laws of the State of Connecticut without
giving effect to principles of conflict of laws.

     Section 7. DEFINED TERMS. Capitalized terms used herein which are not
expressly defined herein shall have the meanings ascribed to them in the
Agreement.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

                                       -3-
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     IN WITNESS WHEREOF, the parties have caused this Amendment to be duly
executed and delivered by their respective officers, as an instrument under
seal, as of the date first above written.

ARCH REINSURANCE LTD.

By: /s/ Janine Trench
   ---------------------------------
  Name: Janine Trench
  Title: Controller

ARCH REINSURANCE COMPANY

By: /s/ John F. Rathgeber
   ---------------------------------
  Name: John F. Rathgeber
  Title: Managing Director and
         Chief Operating Officer

ALTERNATIVE RE LIMITED

By: /s/ Graham B.R. Collis
   ---------------------------------
  Name: Graham B.R. Collis
  Title: Director

ARCH INSURANCE COMPANY

By: /s/ Fred S. Eichler
   ---------------------------------
  Name: Fred S. Eichler
  Title: Senior Vice President and
         Chief Financial Officer

FLEET NATIONAL BANK

By: /s/ Lawrence Davis
   ---------------------------------
  Name: Lawrence Davis
  Title: Portfolio Manager

                                       -4-<Page>

                                                                    EXHIBIT 10.2

                        AMENDMENT TO RETENTION AGREEMENT

     WHEREAS, Arch Capital Group Ltd., a Bermuda company (the "COMPANY"), and
Arch Capital Group (U.S.) Inc., a Delaware corporation and a wholly owned
subsidiary of the Company (the "SUBSIDIARY"), entered into a retention agreement
(the "AGREEMENT"), dated as of January 4, 2002, with Robert Clements (the
"DIRECTOR"); and capitalized terms used without definition herein have the
meanings given to them in the Agreement;

     NOW, THEREFORE, in consideration of the premises and mutual covenants
contained herein, the parties have agreed to amend the Agreement as follows,
effective as of January 1, 2003:

     1.   Section 2(a) of the Agreement shall be amended and restated in its
          entirety as follows:

          "Compensation for the Director's services shall be at an annual
          compensation rate equal to 50% of the then annual base salary of the
          Chief Executive Officer of the Company. The Director may also receive
          an annual cash bonus to be determined by the Board."

     2.   Section 2(b) of the Agreement shall be amended and restated in its
          entirety as follows:

          "Such annual compensation for each year shall be payable in cash on a
          semi-monthly basis."

     3.   Section 2(c) of the Agreement shall be deleted, and the phrase "of the
          Share Portion and Cash Portion" shall be deleted from Section 2(d) of
          the Agreement.

     4.   All other provisions of the Agreement shall remain in full force and
effect. This amendment may be executed in two or more counterparts, each of
which shall constitute one and the same instrument.

     IN WITNESS WHEREOF, the undersigned have executed this agreement on April
10, 2003.

                                       ARCH CAPITAL GROUP LTD.

                                       By:   /s/ John D. Vollaro
                                          ------------------------------------
                                          Name:  John D. Vollaro
                                          Title: Executive Vice President and
                                                 Chief Financial Officer

                                       ARCH CAPITAL GROUP (U.S.) INC.

                                       By:   /s/ Peter A. Appel
                                          ------------------------------------
                                          Name:  Peter A. Appel
                                          Title: Vice Chairman

                                             /s/ Robert Clements
                                       ---------------------------------------
                                       Robert Clements

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