EXECUTION COPY









                      COMMON SECURITIES GUARANTEE AGREEMENT

                                   Viatel, Inc

                           Dated as of April 12, 2000







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                                TABLE OF CONTENTS

                                                                            Page

                                    ARTICLE I
                         DEFINITIONS AND INTERPRETATION

SECTION 1.1.          Definitions Interpretation.............................2

                                   ARTICLE II
                                    GUARANTEE

SECTION 2.1.          Guarantee..............................................3
SECTION 2.2.          Subordination..........................................4
SECTION 2.3.          Waiver of Notice and Demand............................4
SECTION 2.4.          Obligations Not Affected...............................4
SECTION 2.5.          Rights of Holders......................................5
SECTION 2.6.          Guarantee of Payment...................................5
SECTION 2.7.          Subrogation............................................5
SECTION 2.8.          Independent Obligations................................6
SECTION 2.9.          Acknowledgment by Guarantor............................6

                                   ARTICLE III
                    LIMITATION OF TRANSACTIONS; SUBORDINATION

SECTION 3.1.          Limitation of Transactions.............................6
SECTION 3.2.          Ranking................................................7

                                   ARTICLE IV
                                   TERMINATION

SECTION 4.1.          Termination............................................7

                                    ARTICLE V
                                  MISCELLANEOUS

SECTION 5.1.          Successors and Assigns.................................8
SECTION 5.2.          Amendments.............................................8
SECTION 5.3.          Notices................................................8
SECTION 5.4.          Benefit................................................9
SECTION 5.5.          Governing Law..........................................9




NYDOCS01/689470 2

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                      COMMON SECURITIES GUARANTEE AGREEMENT

                  This  COMMON  SECURITIES   Guarantee  Agreement  (the  "Common
Securities Guarantee"), dated as of April 12, 2000, is executed and delivered by
VIATEL, INC., a Delaware  corporation (the "Guarantor"),  for the benefit of the
Holders  (as  defined  herein)  from time to time of the Common  Securities  (as
defined herein) of Viatel Financing Trust I, a Delaware statutory business trust
(the "Trust").

                  WHEREAS,  pursuant to an Amended and Restated  Declaration  of
Trust (the "Declaration"), dated as of April 12, 2000, among the trustees of the
Trust named  therein,  the Guarantor,  as sponsor,  and the holders from time to
time of undivided  beneficial interests in the assets of the Trust, the Trust is
issuing on the date  hereof  92,783.5  common  securities,  having an  aggregate
stated  liquidation  amount of  $4,639,175  designated  the 7 3/4% Trust  Common
Securities (the "Common  Securities") (plus up to an additional  18,556.7 Common
Securities,  having an aggregate liquidation amount of $927,835, to meet capital
requirements  of the Trust in the event of an issuance of Additional  Securities
(as defined in the Placement  Agreement dated April 6, 2000 among Morgan Stanley
& Co., Incorporated,  Salomon Smith Barney Inc., Banc of America Securities LLC,
the  Trust  and  the  Guarantor)),  designated  the 7  3/4%  Convertible  Common
Securities;

                  WHEREAS,  as incentive  for the Holders to purchase the Common
Securities,  the Guarantor desires  irrevocably and unconditionally to agree, to
the extent set forth in this  Common  Securities  Guarantee,  to  guarantee  the
obligations  of the Trust to the Holders of Common  Securities  on the terms and
conditions set forth herein; and

                  WHEREAS,  the  Guarantor is also  executing  and  delivering a
guarantee  agreement (the  "Preferred  Securities  Guarantee") in  substantially
identical  terms to this  Common  Securities  Guarantee  for the  benefit of the
holders of the Convertible Preferred Securities (as defined herein), except that
if an Event of  Default  (as  defined in the  Indenture),  has  occurred  and is
continuing,  the rights of Holders of the Common Securities to receive Guarantee
Payments (as defined  herein) under this Common  Securities  Guarantee  shall be
subordinated  to the  rights of  Holders  of  Preferred  Securities  to  receive
Guarantee Payments (as defined in the Preferred Securities  Guarantee) under the
Preferred Securities Guarantee;

                  NOW,  THEREFORE,  in  consideration  of the  purchase  by each
Holder of Common  Securities,  which purchase the Guarantor  hereby agrees shall
benefit  the  Guarantor,   the  Guarantor  executes  and  delivers  this  Common
Securities Guarantee for the benefit of the Holders.



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                                    ARTICLE I
                         DEFINITIONS AND INTERPRETATION

SECTION 1.1.      DEFINITIONS INTERPRETATION

                  In  this  Common  Securities  Guarantee,  unless  the  context
otherwise requires:

                  (a) capitalized terms used in this Common Securities Guarantee
         but not  defined in the  preamble  above have the  respective  meanings
         assigned to them in this Section 1.1;

                  (b) terms  defined in the  Declaration  as at the date  hereof
         have the same  meaning  when used in this Common  Securities  Guarantee
         unless otherwise defined in the Common Securities Guarantee;

                  (c)  a  term  defined  anywhere  in  this  Common   Securities
         Guarantee has the same meaning throughout;

                  (d) all  references  to "the Common  Securities  Guarantee" or
         "this  Common  Securities  Guarantee"  are to  this  Common  Securities
         Guarantees as modified, supplemented or amended from time to time;

                  (e) all  references  in this Common  Securities  Guarantee  to
         Articles  and  Sections  are to  Articles  and  Sections of this Common
         Securities Guarantee unless otherwise specified;

                  (f) a term  defined  in the Trust  Indenture  Act has the same
         meaning when used in this Common Securities Guarantee, unless otherwise
         defined in this  Common  Securities  Guarantee  or unless  the  context
         otherwise requires;

                  (g) a reference to the singular includes the plural and vice
         versa;

                  (h) a reference to any person shall include its successors and
         assigns;

                  (i) a reference to any agreement or instrument shall mean such
         agreement or instrument as supplemented,  modified, amended, or amended
         and restated, and in effect from time to time; and

                  (j) a reference to any statute, law, rule or regulation, shall
         include any amendments  thereto  applicable to relevant Person, and any
         successor statute, law, rule or regulation.



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                  "Convertible  Debentures" means the 7 3/4% Convertible  Junior
Subordinated  Debentures  due  April  15,  2015  of the  Guarantor  held  by the
Institutional Trustee (as defined in the Declaration).

                  "Convertible   Preferred   Securities"  means  the  securities
representing  preferred  undivided  beneficial  interests  in the  assets of the
Trust.

                  "Guarantee   Payments"   means  the   following   payments  or
distributions,  without duplication,  with respect to the Common Securities,  to
the  extent  not  paid  or  made  by the  Trust:  (i)  any  accrued  and  unpaid
Distributions as defined in the Declaration that are required to be paid on such
Common  Securities to the extent the Trust shall have funds available  therefor,
(ii) the redemption price, including all accrued and unpaid Distributions to the
date of redemption  (the  "Redemption  Price") to the extent the Trust has funds
available therefor,  with respect to any Common Securities called for redemption
by the Trust, and (iii) upon a voluntary or involuntary dissolution,  winding-up
or termination of the Trust (other than in connection  with the  distribution of
Convertible  Debentures  to the Holders in  exchange  for Common  Securities  as
provided in the Declaration or the redemption of all the Common Securities), the
lesser of (a) the aggregate of the liquidation amount and all accrued and unpaid
Distributions on the Common  Securities to the date of payment to the extent the
Trust has funds  available  therefor,  and (b) the amount of assets of the Trust
remaining  available for  distribution to Holders upon  liquidation of the Trust
(in either case,  the  "Liquidation  Distribution").  If an Event of Default (as
defined in the Indenture), has occurred and is continuing, the rights of Holders
of the  Common  Securities  to receive  Guarantee  Payments  under  this  Common
Securities  Guarantee are  subordinated  to the rights of Holders of Convertible
Preferred Securities to receive Guarantee Payments.

                  "Holder" shall mean any holder, as registered on the books and
records of the Trust, of any Common Securities.

                  "Indenture"  means the  Indenture  dated as of April 12,  2000
among the Guarantor and The Bank of New York, a New York banking corporation, as
trustee,  pursuant to which the  Convertible  Debentures are to be issued to the
Institutional Trustee (as defined in the Indenture) of the Trust.


                                   ARTICLE II
                                    GUARANTEE

SECTION 2.1.               GUARANTEE

                  The Guarantor irrevocably and unconditionally agrees to pay in
full to the Holders  the  Guarantee  Payments  (without  duplication  of amounts
theretofore  paid by the Trust),  as and when due,  regardless  of any  defense,
right of  set-off  or  counterclaim  which  the Trust  may have or  assert.  The
Guarantor's obligation to make a Guarantee Payment may be satisfied by direct

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payment of the  required  amounts by the  Guarantor to the Holders or by causing
the Trust to pay such amounts to the Holders.

SECTION 2.2.               SUBORDINATION

                  If an event of default under the Indenture has occurred and is
continuing,  the rights of Holders of the Common Securities to receive Guarantee
Payments under this Common  Securities  Guarantee are subordinated to the rights
of Holders of Convertible  Preferred  Securities to receive  Guarantee  Payments
under the Preferred Securities Guarantee.

SECTION 2.3.               WAIVER OF NOTICE AND DEMAND

                  The  Guarantor  hereby  waives  notice of  acceptance  of this
Common  Securities  Guarantee  and of any  liability  to which it applies or may
apply, presentment,  demand for payment, any right to require a proceeding first
against the Trust or any other Person before  proceeding  against the Guarantor,
protest, notice of nonpayment,  notice of dishonor, notice of redemption and all
other notices and demands.

SECTION 2.4.               OBLIGATIONS NOT AFFECTED

                  The  obligations,  covenants,  agreements  and  duties  of the
Guarantor under this Common Securities  Guarantee shall in no way be affected or
impaired by reason of the happening from time to time of any of the following:

                  (a) the release or waiver,  by operation of law or  otherwise,
         of the performance or observance by the Trust of any express or implied
         agreement,   covenant,   term  or  condition  relating  to  the  Common
         Securities to be performed or observed by the Trust;

                  (b) the  extension of time for the payment by the Trust of all
         or any  portion of the  Distributions,  Redemption  Price,  Liquidation
         Distribution  or any other sums  payable  under the terms of the Common
         Securities  or the extension of time for the  performance  of any other
         obligation  under,  arising out of, or in connection  with,  the Common
         Securities   (other   than  an   extension   of  time  for  payment  of
         Distributions,  Redemption Price, Liquidation Distribution or other sum
         payable that results from the extension of any interest  payment period
         on the Convertible  Debentures or any extension of the maturity date of
         the Convertible Debentures permitted by the Indenture);

                  (c) any failure,  omission,  delay or lack of diligence on the
         part  of  the  Holders  to  enforce,  assert  or  exercise  any  right,
         privilege,  power or remedy  conferred  on the Holders  pursuant to the
         terms of the Common Securities,  or any action on the part of the Trust
         granting indulgence or extension of any kind;


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                  (d) the  voluntary or  involuntary  liquidation,  dissolution,
         sale  of  any   collateral,   receivership,   insolvency,   bankruptcy,
         assignment for the benefit of creditors,  reorganization,  arrangement,
         composition or  readjustment  of debt of, or other similar  proceedings
         affecting, the Trust or any of the assets of the Trust;

                  (e)      any invalidity of, or defect or deficiency in, the
         Common Securities;

                  (f)      the settlement or compromise of any obligation
         guaranteed hereby or hereby incurred; or

                  (g) any other  circumstance  whatsoever  that might  otherwise
         constitute a legal or equitable discharge or defense of a guarantor, it
         being  the  intent  of this  Section  2.4 that the  obligations  of the
         Guarantor  hereunder shall be absolute and unconditional  under any and
         all circumstances.

                  There  shall be no  obligation  of the  Holders  or any  other
Persons to give notice to, or obtain  consent of, the Guarantor  with respect to
the happening of any of the foregoing.

SECTION 2.5.               RIGHTS OF HOLDERS

                  The Guarantor expressly acknowledges that any Holder of Common
Securities may institute a legal  proceeding  directly  against the Guarantor to
enforce  its rights  under  this  Common  Securities  Guarantee,  without  first
instituting a legal proceeding against the Trust or any other Person.

SECTION 2.6.               GUARANTEE OF PAYMENT

                  This  Common  Securities  Guarantee  creates  a  guarantee  of
payment and not of collection.

SECTION 2.7.               SUBROGATION

                  The  Guarantor  shall be  subrogated to all (if any) rights of
the  Holders of Common  Securities  against  the Trust in respect of any amounts
paid to such Holders by the Guarantor  under this Common  Securities  Guarantee;
PROVIDED,  HOWEVER,  that the Guarantor shall not (except to the extent required
by  mandatory  provisions  of law) be entitled to enforce or exercise any rights
that it may acquire by way of  subrogation or any  indemnity,  reimbursement  or
other  agreement,  in all  cases  as a  result  of  payment  under  this  Common
Securities  Guarantee,  if, at the time of any such payment, any amounts are due
and unpaid under this Common Securities  Guarantee.  If any amount shall be paid
to the Guarantor in violation of the preceding sentence, the Guarantor agrees to
hold such  amount in trust for the  Holders  and to pay over such  amount to the
Holders.


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SECTION 2.8.               INDEPENDENT OBLIGATIONS

                  The Guarantor  acknowledges that its obligations hereunder are
independent  of the  obligations  of  the  Trust  with  respect  to  the  Common
Securities  and that the  Guarantor  shall be liable as principal  and as debtor
hereunder  to make  Guarantee  Payments  pursuant  to the  terms of this  Common
Securities Guarantee  notwithstanding the occurrence of any event referred to in
subsections (a) through (g), inclusive, of Section 2.4 hereof.

SECTION 2.9.               ACKNOWLEDGMENT BY GUARANTOR

                  The Guarantor acknowledges its obligation to issue and deliver
common stock,  par value $0.01 per share, of the Guarantor (the "Common Stock"),
upon the conversion of the Common Securities.


                                   ARTICLE III
                    LIMITATION OF TRANSACTIONS; SUBORDINATION

SECTION 3.1.               LIMITATION OF TRANSACTIONS

                  So long as any Common  Securities remain  outstanding,  if (i)
the  Guarantor  has  exercised  its  option to defer  interest  payments  on the
Convertible  Debentures by extending the interest payment period and such period
or extension  thereof,  shall be continuing,  (ii) there shall have occurred any
default by the Guarantor on any of its payment or other  obligations  under this
Common Securities Guarantee or (iii) there shall have occurred and be continuing
any event  that,  with the giving of notice or the lapse of time or both,  would
constitute  an event of default  under the  Declaration,  then the Guarantor (a)
shall not declare or pay  dividends on, make  distributions  with respect to, or
redeem,  purchase or acquire, or make a liquidation payment with respect to, any
of its capital stock,  (b) shall not make any payment of interest,  principal or
premium,  if any, on or repay,  repurchase or redeem any debt  securities of the
Guarantor  that rank PARI PASSU with or junior in  interest  to the  Convertible
Debentures  and (c) shall not make any  guarantee  payments  with respect to any
guarantee  by the  Guarantor of the debt  securities  of any  subsidiary  of the
Guarantor if such  guarantee  ranks PARI PASSU with or junior in interest to the
Convertible  Debentures  (other than (i) a  reclassification  of the Guarantor's
capital  stock or the  exchange  or  conversion  of one  class or  series of the
Guarantor's capital stock for another class or series of the Guarantor's capital
stock;  (ii) the purchase of fractional  interests in shares of the  Guarantor's
capital stock pursuant to the conversion or exchange  provisions of such capital
stock or the security  being  converted  into or exchanged  for the  Guarantor's
capital stock;  (iii) the payment of dividends or  distributions in common stock
of the  Guarantor;  (iv) any  declaration  of a dividend in connection  with the
implementation  of a  stockholders'  rights plan, or the issuance of stock under
any such plan in the future,  or the redemption or repurchase of any such rights
pursuant thereto;  (v) payments under this Common  Securities  Guarantee and the
Preferred Securities  Guarantee;  (vi) purchases of the Guarantor's common stock
related to the issuance of the

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Guarantor's  common stock or rights under any of the  Guarantor's  benefit plans
for the Guarantor's  directors,  officers or employees;  or (vii) obligations of
the Guarantor under any dividend reinvestment and stock purchase plans).


SECTION 3.2.               RANKING

                  (a)  This  Common  Securities  Guarantee  will  constitute  an
         unsecured obligation of the Guarantor and will rank (i) subordinate and
         junior in right of payment to all other  liabilities  of the Guarantor,
         except any  liabilities  that may be made PARI PASSU expressly by their
         terms,  (ii) PARI PASSU with the most senior  preferred  or  preference
         stock now or hereafter  issued by the  Guarantor and with any guarantee
         now or  hereafter  entered  into by the  Guarantor  in  respect  of any
         preferred or preference  stock of any Affiliate of the  Guarantor,  and
         (iii) senior to the Common Stock.

                  (b) The holders of any  obligations  of the Guarantor that are
         senior in priority  to the  obligations  under this  Common  Securities
         Guarantee  will be entitled to all of the rights inuring to the holders
         of "Senior  Indebtedness"  under Article 12 of the  Indenture,  and the
         Holders  of the Common  Securities  will be subject to all of the terms
         and  conditions of such Article 12 with respect to any claims or rights
         hereunder with the same effect as though fully set forth herein.


                                   ARTICLE IV
                                   TERMINATION

SECTION 4.1.               TERMINATION

                  This Common Securities Guarantee shall terminate upon (i) full
payment of the amount payable upon redemption of the Common Securities, (ii) the
distribution  of the  Guarantor's  Common Stock to the Holders in respect of the
conversion of the Convertible  Preferred Securities into the Common Stock or the
distribution  of the Convertible  Debentures (as defined in the  Declaration) to
the Holders of all of the Common Securities or (iii) full payment of the amounts
payable  in  accordance  with the  Declaration  upon  liquidation  of the Trust.
Notwithstanding the foregoing, this Common Securities Guarantee will continue to
be  effective  or will be  reinstated,  as the case  may be,  if at any time any
Holder of Common  Securities  must  restore  payment  of any sums paid under the
Common Securities or under this Common Securities Guarantee.



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                                    ARTICLE V
                                  MISCELLANEOUS

SECTION 5.1.               SUCCESSORS AND ASSIGNS

                  All  guarantees  and  agreements   contained  in  this  Common
Securities Guarantee shall bind the successors, assigns, receivers, trustees and
representatives  of the  Guarantor and shall inure to the benefit of the Holders
of the Common Securities then outstanding.

SECTION 5.2.               AMENDMENTS

                  Except  with  respect to any  changes  which do not  adversely
affect  the rights of  Holders  (in which  case no  consent  of Holders  will be
required),  this Common Securities  Guarantee may only be amended with the prior
approval of the Holders of at least a majority in liquidation  amount of all the
outstanding Common Securities. The provisions of Section 12.2 of the Declaration
with  respect to  meetings of Holders of the  Securities  apply to the giving of
such approval.

SECTION 5.3.               NOTICES

                  All notices provided for in this Common  Securities  Guarantee
shall be in writing,  duly signed by the party giving such notice,  and shall be
delivered,  sent by  facsimile  or mailed by  registered  or  certified  mail or
overnight courier, as follows:

                  (a) if given to the Trust, in care of the Regular  Trustees at
         the Trust's  mailing  address set forth below (or such other address as
         the Trust may give notice of to the Holders of the Common Securities):

                  c/o Viatel, Inc.
                  685 Third Avenue
                  24th Floor
                  New York, New York  10017
                  Attention:  General Counsel

                  (b) if  given to the  Guarantor,  at the  Guarantor's  mailing
         address set forth  below (or such other  address as the  Guarantor  may
         give notice of to the Holders of the Common Securities):

                  Viatel, Inc.
                  685 Third Avenue
                  24th Floor
                  New York, New York  10017
                  Attention:  General Counsel

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                  (c) if  given  to any  Holder  of  Common  Securities,  at the
         address set forth on the books and records of the Trust.

                  All such  notices  shall be  deemed to have  been  given  when
received in person,  telecopied with receipt confirmed, or mailed by first class
mail,  postage  prepaid  except  that if a notice or other  document  is refused
delivery or cannot be delivered  because of a changed address of which no notice
was given,  such notice or other document shall be deemed to have been delivered
on the date of such refusal or inability to deliver.

SECTION 5.4.               BENEFIT

                  This Common Securities  Guarantee is solely for the benefit of
the Holders of the Common Securities and is not separately transferable from the
Common Securities.

SECTION 5.5.               GOVERNING LAW

                  THIS COMMON SECURITIES GUARANTEE SHALL BE GOVERNED BY
AND CONSTRUED IN ACCORDANCE WITH THE INTERNAL LAWS OF THE STATE OF
NEW YORK.



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                  THIS COMMON SECURITIES  GUARANTEE  AGREEMENT is executed as of
the day and year first above written.

                                          VIATEL, INC.,
                                          as Guarantor



                                          By: /s/ James P. Prenetta
                                             ------------------------------
                                             Name:  James P.Prenetta
                                             Title: Senior Vice President and
                                                      General Counsel


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