Rule 424(b)(3) of the Securities Act of 1933
                                   Registration Statement 333-50111

PROSPECTUS SUPPLEMENT NO. 10
(TO PROSPECTUS DATED JUNE 4, 1998)

                           AMERICAN TOWER CORPORATION

         This Prospectus Supplement No. 10 supplements the Prospectus dated June
4,  1998  of  American  Tower  Corporation,   formerly  American  Tower  Systems
Corporation  ("ATC" or the  "Company"),  with  respect to the filing on July 16,
1999, of a Current Report on Form 8-K, which is attached hereto.

Any statement  contained in the Prospectus as heretofore  supplemented  shall be
deemed to be modified or superseded to the extent that a statement  contained in
the Form 8-K  modifies or  supersedes  such  statement.  Any such  statement  so
modified or superseded shall not be deemed, except as so modified or superseded,
to constitute a part of the Prospectus.

                            ------------------------


                Prospectus Supplement No. 10, dated July 16, 1999




SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): July 16, 1999 (June 28, 1999) AMERICAN TOWER CORPORATION (Exact name of registrant as specified in its charter) Delaware 001-14195 65-0723837 (State or Other Jurisdiction (Commission (IRS Employer of Incorporation) File Number) Identification No.) 116 Huntington Avenue Boston, Massachusetts 02116 - -------------------------------------------------------------------------------- (Address of Principal Executive Offices) (Zip Code) (617) 375-7500 ------------------------------------------------------- (Registrant's telephone number, including area code)

Item 5. Other Events. On June 28, 1999, American Tower Corporation (the "Company" or "ATC") entered into an Agreement and Plan of Merger (the "Merger Agreement") with UniSite, Inc. ("UniSite"), and ATI Merger Corporation, a subsidiary of ATC and a Delaware corporation ("ATI"), pursuant to which UniSite will merge with and into ATI, with UniSite being the surviving corporation (the "Merger"). UniSite was founded in 1994 to address the challenges associated with antenna siting and to focus primarily on tower site management. Most recently, UniSite has expanded its scope to include site ownership and development. UniSite presently owns approximately 400 towers suited for colocation and has an exclusive build-to-suit contract with Omnipoint Corporation through the year 2012. Pursuant to the Merger Agreement, which has been approved by the Board of Directors of ATC and UniSite, and was approved by the stockholders of UniSite by written consent on July 12, 1999, UniSite preferred and common stockholders will receive an aggregate of approximately $165 million in cash, subject to working capital and completed tower closing adjustments. Pursuant to the Merger, ATC will also assume approximately $40 million in debt, subject to adjustment for interim acquisitions and capital expenditures. Consummation of the Merger is expected to occur on the earlier of (a) January 31, 2000, or (b) UniSite's owning and operating 600 wireless communication towers, subject to certain conditions including, the expiration or early termination of the waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended. For more information, see the ATC press release, dated June 28, 1999, which is attached herewith as Exhibit 99.1. Item 7. Financial Statements, Pro Forma Financial Information and Exhibits. (a) Financial Statements In accordance with Item 7(a)(4) of Form 8-K, such financial statements shall be filed in a Current Report on Form 8-K no later than 75 days after the consummation of the Merger. (b) Pro Forma Financial Information As of the date of this filing of this Current Report on Form 8-K, it is impracticable for the Company to provide the pro forma financial information required by this Item 7(b). In accordance with Item 7(b) of Form 8-K, such financial statements shall be filed in a Form 8-K no later than 75 days after the consummation of the Merger. (c) Exhibits Exhibit 2.1 - Agreement and Plan of Merger, dated as of June 28, 1999, by and among American Tower Corporation, a Delaware corporation, ATI Merger Corporation, a Delaware corporation and UniSite, Inc., a Delaware corporation. Exhibit 99.1 - Press Release, dated as of June 28, 1999.

SIGNATURES Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized. AMERICAN TOWER CORPORATION (Registrant) Date: July 16, 1999 By: /s/ Justin D. Benincasa Name: Justin D. Benincasa Title: Vice President and Corporate Controller